NRLF 


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GIFT  OF 
AU  //.  T 


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THE 


PRACTICAL  MANAGEMENT 


OF 


DYNAMOS  AND  MOTORS 


BY       /.  i  .,v  '.     J< 
FRANCIS  B.   CROgKEK, 

ADJUNCT  PROFESSOR  OF  ELECTRICAL  ENGINEERING,  COLUMBIA  COLLEGE,   N.  Y.J 

VICE-PRES.   OF    THE    AMER.   INST?   OF    ELEWTRICAL    ENGINEERS; 

PRES.   OF  THE  NEW  YORK  ELECTRICAL  SOCIETY; 

'  AND 

SCHUYLER  S.   WHEELER,  D.Sc. 

ELECTRICAL  EXPERT  OF   THE  BOARD  OF  ELECTRICAL  CONTROL,  NEW  YORK  CITY; 

PAST  VICE-PRES.  OF  THE  AMER.  INST.  OP  ELECTRICAL  ENGINEERS; 

MEMBER    AMERICAN     SOCIETIES     OF     CIVIL   AND 

MECHANICAL  ENGINEERS. 


NEW  YORK  : 
D.  VAN  NOSTRAND  COMPANY, 

23  MURRAY  AND  27  WARREN  ST. 

LONDON: 

E.  &  F.  N.  SPON,  125  STRAND. 
1892 


COPYRIGHT,  1892, 

BY 
D.  VAN  NOSTRAND  COMPANY. 


7^  "  7 


PREFACE. 


THE  contents  of  this  book  appeared  as  a  series  of  arti- 
cles in  the  Electrical  Engineer  between  September  1891 
and  May  1892.  Its  object  is  to  give  simple  directions  for 
the  practical  use  and  management  of  dynamos  and  motors. 

The  authors  have  taken  special  care  to  arrange  the  ma- 
terial so  that  the  different  subjects  are  treated  separately 
and  in  the  proper  order,  and  the  headings  are  printed  in 
heavy  type  to  facilitate  ready  reference  to  any  subdivision. 

The  reader  is  recommended  to  familiarize  himself  at 
first  with  the  plan  and  contents  of  the  book,  that  he  may 
be  able  to  turn  readily  to  any  part  of  the  book  wanted 
when  at  work. 

The  authors  design  the  present  volume  to  be  simply  the 
ground-work  of  a  larger  and  more  elaborate  treatment  of 
the  subject  which  they  contemplate  preparing  and  they 
will  appreciate  any  suggestions. 

NEW  YORK,  May,  1892. 


464543 


CONTENTS. 


PAET  I. 

PAGE 

INTRODUCTION.  . .  1 


CHAPTER  I. 

GENERAL  PRINCIPLES  OF  DYNAMOS  AND  MOTORS. 

Definition!.  Principles  of  Action.  Similarity  of  Dynamos  and 
Motors.  General  Form.  Armature.  Field-magnet 3 

CHAPTER  II. 

SELECTING  DYNAMOS  AND   MOTORS. 

Construction.  Finish.  Simplicity.  Attention  Required.  Hand- 
ling. Regulation.  Armature.  Capacity.  Form.  Weight. 
Cost.  The  Various  Kinds  of  Circuits 5 

CHAPTER  III. 

INSTALLING   DYNAMOS   AND    MOTORS. 

Setting  Up.  Pulleys.  Belting.  Electrical  Connections. 
Wiring.  Switches  and  Cut-outs.  Diagrams  of  Connec- 
tions. Shunt  Dynamo  on  Constant-potential  Circuit. 
Series  Dynamo  on  Constant-current  Circuit.  Alter- 
nating-current Plant 9 

v 


vi  Contents. 

CHAPTER  IV. 

STARTING  DYNAMOS  AND  MOTORS. 

PAGE 

General.  Starting  a  Dynamo.  Coupling  Dynamos  together. 
Dynamos  in  Parallel.  Series-wound  Dynamos  in  Parallel. 
Compound  Dynamos  in  Parallel.  Alternators  in  Parallel. 
Dynamos  in  Series.  Shunt  or  Compound  Dynamos  in 
Series.  Series- wound  Dynamos  in  Series.  Alternators  in 
Series.  Dynamos  on  the  Three-wire  System.  Starting  Mo- 
tors. Constant-potential  Motors  (Shunt-wound).  Con- 
stant-potential Motors  (Series-wound).  Constant-potential 
Motors  (Differentially  wound).  Constant-current  Motors. 
Alternating-current  Motors 23 

CHAPTER  V. 

RUNNING  DYNAMOS  AND  MOTORS. 

General  Instructions.     Personal  Safety 41 

CHAPTER  VI. 

STOPPING  DYNAMOS  AND   MOTORS. 

One  Constant-potential  Dynamo.  Dynamos  in  Parallel.  Com- 
pound Dynamos  in  Parallel.  Dynamos  on  the  Three-wire 
System.  Constant-current  Dynamos  and  Motors.  One 
Alternator.  Alternators  in  Parallel.  Constant-potential 
Motor , 44 

CHAPTER  VH. 

TESTING  DYNAMOS   AND   MOTORS. 

Adjustment.  Mechanical  Strength.  Friction.  Balance. 
Noise.  Electrical  Resistance.  Voltage.  Current.  Speed. 
Torque  or  Pull.  Power.  Efficiency.  Heating.  Spark- 
ing. Magnetism.  Line  or  Circuit  Testing 47 


Contents.  vii 


PART  II. 

THE  LOCALIZATION  AND  REMEDY  OF  TROUBLES 
IN  DYNAMOS  AND  MOTORS. 

PAGE 

INTRODUCTION 1 

CHAPTER  I. 
SPARKING  AT  COMMUTATOR 5 


CHAPTER  II. 
HEATING  IN  DYNAMO  OR  MOTOR.    GENERAL  INSTRUCTIONS..     11 

CHAPTER  III. 
HEATING  OF  ARMATURE «, 13 

CHAPTER  IV. 
HEATING  OF  FIELD-MAGNETS 14 

CHAPTER  V. 
HEATING  OF  BEARINGS 16 

CHAPTER  VI. 
NOISE 21 

CHAPTER  VII. 
SPEED  TOO  HIGH  OR  Low 25 

CHAPTER  VIII. 
MOTOR  STOPS  OR  FAILS  TO  START 27 

CHAPTER  IX. 
DYNAMO  FAILS  TO  GENERATE 30 


THE 


PRACTICAL     MANAGEMENT 

OF 

DYNAMOS    AND    MOTORS. 


INTRODUCTION. 


THE  purpose  of  these  articles  is  to  set  forth  the  more  im- 
portant facts  which  present  themselves  in  the  actual  hand- 
ling of  dynamo-electric  machines  and  electric  motors,  as 
a  guide  for  those  who  use  or  study  these  machines.  The 
authors  do  not  claim  for  this  treatment  of  the  subject  that 
it  is  anything  more  than  a  set  of  directions  in  which  the 
various  points  are  arranged  under  headings  for  convenience 
of  reference. 

The  subjects  considered  are  :  Chapter  I,  General  Princi- 
ples of  Dynamos  and  Motors  ;  Chapter  II,  Directions  for 
Selecting  ;  Chapter  III,  Installing  ;  Chapter  IV,  Starting  ; 
Chapter  V,  Running  ;  Chapter  VI,  Stopping  ;  and  Chap- 
ter VII,  Testing  .Dynamos  arid  Motors;  also  Part  II, 
Directions  for  Locating  and  Remedying  Troubles  in  these 
machines. 

Heretofore  writers  on  the  dynamo  or  motor  have  usually 
treated  these  machines  entirely  distinctly,  and  books  or 
papers  on  the  dynamo  usually  contain  nothing  about  the 
motor,  or  merely  consider  it  briefly  in  a  few  special  chap- 
ters, and  books  on  the  motor  only  refer  to  the  dynamo  in- 


2  Practical  Management  of 

cidentally.  The  authors  have  found  that  there  is  no  ne- 
cessity for  this  separation  ;  in  fact,  nine  out  of  ten 
statements  which  apply  to  the  dynamo  are  equally  ap- 
plicable to  the  motor,  and  if  the  word  machine  is  used  in- 
stead of  dynamo,  the  statement  covers  both  and  becomes 
doubly  important  and  useful.  Occasionally,  of  course,  it 
is  necessary  to  distinguish  between  the  two  machines,  but, 
as  a  matter  of  fact,  the  difference  in  treatment  required 
for  dynamos  and  motors  is  often  less  than  for  different 
kinds  of  dynamos;  for  example,  a  shunt  dynamo  and  series 
dynamo  differ  from  one  another  much  more  than  do  a 
shunt  dynamo  and  shunt  motor. 


Dynamos  and  Motors.  3 

CHAPTER  I. 

GENERAL    PRINCIPLES    OF    DYNAMOS    AND    MOTORS. 

Definitions* — A.  dynamo- electric  machine  is  a  ma- 
chine for  converting  mechanical  energy  into  electrical  en- 
ergy•  in  other  words,  it  generates  electric  current  when 
driven  by  mechanical  power.  The  term  dynamo -electric 
machine  is  so  long  that  it  is  usually  and  unavoidably 
shortened  into  "  dynamo,"  which  has  exactly  the  same 
meaning.  The  name  "electric  generator"  or  simply  "gen- 
erator" is  often  applied  to  the  dynamo,  especially  when 
used  to  produce  current  for  electric  railway  or  other  motors, 
but  this  distinction  is  merely  for  convenience.  An  alter- 
nating-current dynamo  is  commonly  called  an  "  alternator." 
/  An  electric  motor  is  a  machine  for  converting  electrical 
I  energy  into  mechanical  energy;  in  other  words,  it  pro- 
\  duces  mechanical  power  when  supplied  with  an  electric 
current.  An  electric  motor  is  usually  called  simply  a 
motor,  and  although  motor  might  mean  anything  produc- 
ing motion,  it  is  very  rarely  used  in  any  other  sense  and  is 
perfectly  definite  in  connection  with  electrical  matters. 

Principles  of  Action. — The  dynamo  is  based  upon 
the  discovery  made  by  Faraday  in  1831,  that  an  electric 
current  is  generated  in  a  conductor  by  moving  it  in  a  mag- 
netic field.  The  electric  motor  works  on  the  principle  that 
a  conductor  carrying  a  current  in  a  magnetic  field  tends  to 
move.  Thus  it  will  be  seen  from  the  above  statements 
that  the  dynamo  and  motor  are  exactly  the  reverse  of  each 
other  in  their  action. 

Similarity  of  Dynamos  and  Motors. — The 

two  machines  are,  however,  very  similar  in  their  construe- 


4  Practical  Management  of 

tion.  In  fact,  the  same  machine  can  be  used  for  either 
purpose  equally  well.  In  practice  there  are  sometimes 
slight  differences  between  dynamos  and  motors,  as  will  be 
explained  further  on,  but  these  are  not  very  important. 
Hence,  as  already  stated  in  the  introduction,  the  two  ma- 
chines will  be  treated  as  one,  except  where  some  distinc- 
tion is  specially  stated. 

General  Form. — We  have  seen  that  both  the  dy- 
namo and  motor  depend  for  their  action  upon  the  move- 
ment of  conductors  in  magnetic  fields.  Now  it  has  been 
found  as  a  result  of  scientific  experiment  and  practical  ex- 
perience during  the  60  years  since  Faraday's  discovery, 
that  the  best  way  to  carry  out  this  principle  is  to  arrange 
the  conductors  in  suitable  form  and  rotate  them  between 
the  poles  of  a  magnet,  or  magnets.  This  rotating  part  is 
called  the  armature  and  the  magnet  is  called  the  field 
magnet.  In  alternating-current  dynamos  this  plan  is  some- 
times reversed,  the  field  magnets  being  made  to  rotate  and 
the  armature  being  fixed. 

Armature. — This  usually  consists  of  an  armature 
core  of  iron  on  which  are  wound  or  attached  the  conductors 
which  carry  the  current.  This  core  should  be  split  up  or 
laminated,  that  is,  made  of  discs,  tape  or  wire,  of  iron 
separated  by  paper,  varnish  or  rust,  instead  of  one  solid 
piece;  otherwise  it  will  have  useless  currents  generated  in 
it  which  would  waste  the  power  of  the  machine.  This 
core  is  almost  always  made  either  in  the  form  of  a  drum 
or  a  ring,  and  hence  we  have  these  as  the  two  principal 
types  of  armature. 

Field  Magnet. — This  consists  of  one  or  more  iron  cores 
on  which  are  wound  the  field  coils.  Attached  to  th«  field 
cores  are  the  pole-pieces  which  form  the  magnetic  field  or 
space  in  which  the  armature  revolves. 


Dynamos  and  Motors.  5 

CHAPTER  II. 

DIRECTIONS    FOR  SELECTING  DYNAMOS  AND  MOTORS. 

The  choice  of  a  dynamo  or  motor  will,  of  course,  depend 
largely  upon  the  circumstances  in  each  particular  instance. 
There  are,  however,  certain  general  facts  which  apply  to 
almost  all  cases. 

Construction. — This  should  be  of  the  most  solid 
character  and  first-class  in  every  respect,  including  material 
and  workmanship,  both  of  which  should  be  of  the  best 
possible  quality.  All  the  parts  should  be  of  adequate  size 
and  strength  to  insure  durability. 

Finish. — What  is  called  a  fine  finish  on  a  machine  w 
also  very  desirable,  first,  because  it  indicates  good  con- 
struction, and  its  absence  indicates  poor  construction  (there 
is  no  essential  reason  for  this,  but  it  seems  to  be  a  fact  in 
most  cases),  and  second,  it  usually  causes  a  machine  to 
receive  much  better  treatment. 

Simplicity. — The  machine  and  all  its  parts  should  be 
as  simple  as  possible,  and  any  very  peculiar  or  complicated 
part  or  attachment  should  be  avoided.  These  are  some- 
times successful  but  should  be  well  tried  and  proved  before 
accepting. 

Attention. — The  amount  of  attention  required  by  the 
machine  should  be  small ;  for  example,  the  brushes  should 
be  capable  of  being  easily  and  securely  adjusted,  and  the 
oiling  devices  should  be  effective  and  reliable,  self-oiling 
bearings  being  very  desirable.  The  screws,  connections 
and  other  small  parts  should  be  arranged  so  that  they  are 
not  liable  to  become  loose,  and  the  delicate  parts  should 


6  Practical  Management  of 

not  be  particularly  exposed  or  liable  to  injury.  The  ma- 
chine should  be  made  so  as  to  be  easily  and  thoroughly 
cleaned. 

Handling.  —  The  machine  should  be  provided  with 
rings  or  other  means  by  which  it  can  be  easily  lifted  or 
moved  without  injury.  It  should  be  possible  to  take  out 
the  armature  conveniently  by  removing  one  of  the  bearings. 


*  —  Some  form  of  regulator  should  be  pro- 
vided by  which  the  E.  M.  F.  or  current  of  a  dynamo  or  the 
speed  of  a  motor  can  be  reliably  and  accurately  governed. 

Armature.  —  This  should  turn  very  freely  in  the 
bearings,  and  should  be  perfectly  balanced  so  as  not  to 
have  any  appreciable  jar  or  vibration  at  full  speed.  There 
should  be  a  uniform  clearance  of  at  least  -^  inch  all  around 
between  the  armature  and  pole-pieces.  The  armature 
should  be  capable  of  moving  lengthwise  in  the  bearings  at 
least  -J  inch.  It  is  not  usually  desirable  to  have  the  speed 
of  an  armature  at  its  circumference  more  than  3,000  feet 
per  minute.  The  ring-form  of  armature  is  especially 
suited  to  high  voltage  since  the  coils  differing  most  in  po- 
tential are  at  the  greatest  distance  apart.  A  section  of  a 
ring  armature  can  also  be  more  easily  rewound  than  in  the 
case  of  a  drum  armature. 

Capacity.  —  This  should  be  ample  in  all  cases.  It  is  a 
very  common  mistake  to  underestimate  the  work^  required 
of  a  given  machine,  and,  even  if  the  machine  has  'sufficient 
power  at  first,  the  demands  upon  it  are  apt  to  increase  and 
finally  overload  it.  No  one  is  ever  likely  to  regret  choosing 
a  dynamo  or  motor  with  a  considerable  margin  of  capacity, 
since  these  machines  only  consume  power  in  proportion  to 
the  work  they  are  doing.  For  example,  a  30  h.  p.  ma- 
chine would  probably  run  with  a  20  h.  p.  load  more 
economically  and  satisfactorily  than  a  20  h.  p.  machine  with 
the  same  load. 


Dynamos  and  Motors.  7 

Form. — The  machine  should  be  symmetrical,  well  pro- 
portioned, compact  and  solid  in  form.  If  it  is  either  very 
tall  or  very  flat  it  is  usually  inconvenient  and  clumsy.  No 
part  of  the  machine  should  project  excessively,  or  be 
awkwardly  formed  or  arranged.  The  large  and  heavy 
portions  of  the  machine  should  be  placed  as  low  as  possible 
to  give  great  stability.  For  the  same  reason  the  shaft 
should  not  be  high  above  the  base,  nor  should  it  be  so  low 
that  there  is  not  ample  room  for  the  pulley  or  other  at- 
tachment. A  horizontal  belt,  for  example,  will  sag  and 
strike  the  floor  if  the  pulley  is  very  low. 

Weiffht. — The  common  idea  that  it  is  desirable  to  have 
a  very  light  dynamo  or  motor  is  a  mistake  when  it  is  for 
stationary  use.  There  is  no  advantage  in  a  light  machine 
for  stationary  work,  and  it  has  the  disadvantages  of  being 
less  strong,  less  durable  and  less  steady  in  running.  A 
sufficient  weight  to  make  the  machine  thoroughly  sul> 
stantial  is  obviously  a  great  benefit. 

Cost. — It  is  also  a  mistake  to  select  a  cheap  machine, 
since  both  the  materials  and  workmanship  required  in  a 
high  quality  dynamo  or  motor  cost  more  than  in  almost 
any  other  machine  of  the  same  size  and  weight. 

The  Various  Kinds  of  Circuits  on  which  dy- 
namos and  motors  are  commonly  used,  and  the  best  type 
of  machine  in  each  case,  is  as  in  the  tables  on  page  8. 

These  suggestions  as  to  selecting  a  dynamo  or  motor 
may  be  followed  when  it  is  possible  to  make  only  a  general 
examination  of  the  machine,  or  even  in  cases  where  it  is 
only  possible  to  obtain  a  drawing  or  description  of  it.  If 
it  is  desired  to  make  a  complete  investigation  of  the  ma- 
chine, it  is,  of  course,  necessary  to  make  a  thorough  test 
and  measure  exactly  its  various  constants.  This  can  be 
done  as  completely  as  may  be  required  by  following  the 
Directions  for  Testing,  which  are  given  in  another  chapter. 

A  satisfactory  test  cannot  usually  be  made,  however,  until 


8 


Practical  Management  of 


after  the  machine  is  set  up  in  place;  and,  moreover,  it  is 
not  generally  necessary  if  the  machine  is  obtained  from  a 
reputable  source. 


CONSTANT  POTENTIAL. 


(Circuits  on    which  potential  or  voltage  is   kept  constant,  ma- 
chines, lamps,  etc.,  run  in  parallel.) 


Circuits 
intended  for  — 

Potential. 

Dynamo 
should  be  — 

Motor 
should  be  — 

Incandescent 
lisrhtinfir 

f    110  volts    "] 
J  (2-wiresys.)  1 
]     220  volts     f 

Plain  shunt 
or 
compound 

Plain  shunt 
wound 

Electric  railway. 
Power  circuits.... 

[(3-wiresys.)J 
500  volts,    j 

wound. 

Plain  shunt  or 
compound 
wound. 

Series  wound 
for  railway. 
Shunt  wound 
for  stationary. 

CONSTANT   CURRENT. 


(Circuits  on  which  current  or  amperes  are  kept  constant,  machines, 
lamps,  etc.,  run  in  series.) 


Circuits 
intended  for  — 

Current 
in  Amperes. 

Dynamo 
should  be— 

Motor 
should  be— 

Arc  lighting.  .  .  . 
Power  circuits.  . 

1         6.8 
9.5 
f.        or 

J        18 

Series  wound 
with  current 
regulator. 

Series  wound 
with  speed 
regulator. 

Dynamos  and  Motors.  9 

CHAPTER  III. 

DIRECTIONS    FOR    INSTALLING    DYNAMOS    AND    MOTORS. 

Setting  wp. — The  place  selected  for  a  dynamo  or 
motor  should  be  dry,  clean,  cool,  away  from  all  pipes  if 
possible,  where  the  machine  is  in  plain  sight  and  is  easily 
accessible  and  taken  care  of.  Avoid  particularly  any  dusty, 
wet  or  hot  location.  Any  place  near  which  grinding, 
filing,  turning  or  similar  work  is  likely  to  be  done,  is  very 
undesirable  for  a  dynamo  or  motor,  as  the  dust  and  chips 
produced  are  liable  to  injure  the  bearings,  commutator  and 
insulation  of  the  machine.  A  firm  and  level  foundation 
should  be  provided  in  any  case,  and  larger  machines  of  20 
h.  p.  or  more  should  be  set  on  solid  stone,  brick  or  timber 
foundations.  It  is  well,  particularly  in  the  case  of  high- 
voltage  machines,  to  have  them  placed  upon  an  insulating 
base-frame  of  wood,  the  pores  of  which  should  be  filled 
with  paraffine  or  well  varnished  to  keep  out  moisture.  If 
a  wooden  belt-tightening  base  is  used  this  will  answer  the 
purpose,  but  if  iron  tracks  are  used  they  should  be  placed 
on  a  wooden  base-frame.  Fig.  1. 

In  unpacking  and  putting  the  machines  together  the 
greatest  possible  care  should  be  used  in  avoiding  the  least 
injury  to  any  part,  in  scrupulously  cleaning  each  part 
and  in  putting  the  parts  together  in  exactly  the  right  way. 
This  care  is  particularly  important  with  regard  to  the  shaft, 
bearings,  magnetic  joints  and  electrical  connections  from 
which  every  particle  of  grit,  dust,  chips  of  metal,  &c., 
should  be  removed.  It  is  very  desirable  to  have  machinery 
put  together  by  a  person  thoroughly  familiar  with  its  con- 
struction, and  in  the  absence  of  such  a  person  no  one 
should  attempt  it  without  at  least  a  drawing  or  photograph 


10 


Practical  Management  of 


of  the  complete  machine  as  a  guide.  An  exception  may  be 
made  to  this  rule  if  the  machine  is  very  simple  and  the 
way  to  put  it  together  is  perfectly  obvious,  but  in  no  event 
should  the  installation  or  management  of  machinery  be 
left  to  guess-work.  The  armature  should  be  handled  with 
the  greatest  possible  care  in  order  to  avoid  injury  to  the 
wires  and  their  insulation,  as  well  as  to  the  commutator  and 
shaft.  Handle  and  support  the  armature  as  far  as  possible 
by  the  shaft  and  avoid  any  strain  on  the  armature  body  or 
commutator.  If  it  is  necessary  to  lay  the  armature  on  the 
ground,  interpose  a  pad  of  cloth,  but  it  is  much  better  to 


FIG.  1.— BASE  FRAME. 


rest  the  shaft  on  two  wooden  horses  or  other  supports.  A 
convenient  form  of  sling  for  handling  armatures  is  shown 
in  Fig.  2 . 

Pulleys. — A  dynamo  or  motor  is  usually  furnished  by 
the  maker  with  a  pulley  suited  to  it.  In  the  case  of  a 
dynamo,  do  not  use  a  smaller  pulley,  and  with  a  motor  do 
not  use  a  larger  one  without  consulting  a  competent  elec- 
trical engineer.  The  size  of  pulley  required  on  the  other 
machine  or  counter-shaft  to  which  the  given  machine  is  to 
be  connected  is  found  by  multiplying  the  revolutions  per 
minute  of  the  dynamo  or  motor  by  the  diameter  of  its 


Dynamos  and  Motors.  11 

pulley  expressed  in  inches  and  dividing  by  the  revolutions 
per  minute  required  of  the  other  shaft,  which  gives  diame- 
ter of  pulley  in  inches.  The  proper  speed  for  a  dynamo  or 
motor  should  always  be  obtained  from  its  manufacturers, 
and  this  speed  should  not  be  departed  from  without  their 


FIG.  2. — SLING  FOR  HANDLING  ARMATURE, 

approval.  A  simple  rule  for  determining  the  sizes  and 
speeds  in  any  belt  or  gear  transmission  is  that  the  speed  of 
one  pulley  or  gear  wheel  multiplied  by  its  diameter  must 
be  equal  to  the  speed  of  the  other  multiplied  by  its  diame- 
ter. An  allowance  should  be  made  of  one  or  two  per  cent, 
loss  of  speed  in  the  driven  pulley  owing  to  the  slip  of  the 


12 


Practical  Management  of 


belt.  In  fact,  the  usual  result  is  that  the  speed  actually 
obtained  in  practice  is  less  than  is  expected  and  this  often 
makes  a  change  of  pulleys  necessary. 


t  —  The  kind  of  belting  selected  is  somewhat  a 
matter  of  taste  but  "  light  double  "  leather  belting  is  ap- 
plicable to  most  cases  and  is  generally  satisfactory.  The 
width  of  belting  is  usually  made  about  half  an  inch  less 
than  the  face  of  the  pulley  on  the  dynamo  or  motor.  The 
common  rule  for  determining  width  of  belt  is  that 
"single  "  belt  will  transmit  1  h.  p.  for  each  inch  in  width 
at  a  speed  of  1,000  feet  per  minute.  If  the  speed  is  greater 
or  less,  the  power  is  correspondingly  increased  or  de- 
creased. 

This  is  based  upon  the  condition  that  the  belt  is  in  con- 
tact with  the  pulley  around  half  its  circumference  or  180°. 
If  the  arc  of  contact  is  less  than  half  a  circle  the  power 
transmitted  is  less,  as  shown  in  the  accompanying  table  : 


Arc  of  contact 

Fraction  of 

Power  trans- 

of belt. 

circle. 

mitted,  C. 

180° 

H 

1.00 

157^ 

T?ff 

.92 

135 

1 

.84 

112V«> 

J5 

.76 

90  ' 

k 

.64 

The  complete  formula  is,  therefore,  H.  P.  = 


w  X   s   X   c 
lOuO 


that  is,  the  horse  power  transmitted  by  a  belt  is  equal  to 
the  width  of  belt  in  inches  (w)  multiplied  by  the  speed  of 
belt  in  feet  per  minute  (s)  and  by  the  figure  depending 
upon  the  arc  of  contact  (c)  and  divided  by  1000.  For 
example,  a  belt  six  inches  wide  traveling  at  1,500  feet  per 


METHOD  OF  LACING  A  BELT. 

The  smooth  side  of  the  leather  of  the  belt  goes  against  the  pulley.    The 
dotted  lines  represent  the  lacing  on  the  side  away  from  pulley. 

To  face  page  13. 


Dynamos  and  Motws.  13 

minute  and  touching  three-eighths  of  the  circumference  of 
the  pulley  will  transmit: 

6  X  1500  X  .84       7560 

--      =  1000  =  7'56  h'  p- 


"Double"  belting  is  expected  to  transmit  one  and  one- 
half,  and  "  light  double  "  one  and  one-quarter  times,  as 
much  power  as  "  single  "  belting,  of  which  75  sq.  ft.  per 
minute  transmits  one  h.  p. 

The  smooth  side  of  a  belt  should  be  run  against  the  pul- 
ley, as  it  transmits  more  power  and  wears  better.  An  end- 
less belt  should  be  used  for  dynamos  and  motors,  since  they 
usually  run  at  high  speeds.  If  an  endless  belt  is  not  used, 
the  joint  should  be  very  carefully  laced  so  as  to  make  it  as 
straight  and  smooth  as  possible.  In  lacing  belts  there 
must  always  be  as  many  stitches  of  the  lacer  slanting  to 
the  left  as  there  are  to  the  right.  Otherwise  the  ends  of 
the  belt  will  shift  sidewise,  owing  to  the  unequal  strain, 
and  the  projecting  corners  will  catch  on  something.  Two 
good  ways  of  doing  this  are  shown  in  Fig.  3.  In  plan  A 
two  rows  of  oval  holes  should  be  made  with  a  punch  as 
indicated.  The  nearest  hole  should  be  three-quarters  inch 
from  the  side,  and  the  first  row  seven-eighths  inch  from  the 
end,  and  the  second  row  If  inches  from  the  end  of  the  belt. 
In  large  belts  these  distances  should  be  a  little  greater.  A 
regular  belt  lacing  (a  strong,  pliable  strip  of  leather)  should 
be  used,  beginning  at  hole  No.  1  and  passing  consecutively 
through  all  the  holes  as  numbered. 

In  plan  B  the  holes  are  all  made  in  a  row.  This  plan  has 
the  advantage  of  making  the  lacers  lie  parallel  with  the 
motion  on  the  pulley  side.  The  lacing  is  doubled  to  find 
its  middle,  and  the  two  ends  are  passed  through  the  two 
holes  marked  "]_"  and  "  1A,"  precisely  as  in  lacing  a  shoe. 
The  two  ends  are  then  passed  successively  through  the  two 
series  of  holes  in  the  order  in  whicli  they  are  numbered, 
2,  3,  4,  etc.,  and  2  A,  3  A,  4  A,  etc.,  finishing  at  13  and  13  A, 


14  Practical  Management  of 

which  are  additional  holes  for  fastening  the  ends  of  the 
lacer. 

A  six-inch  belt  should  have  seven  holes  on  each  part ; 
other  widths  in  proportion.  Be  very  careful  to  measure 
correctly  the  length  of  belt  required,  as  it  is  very  awkward 
to  have  it  too  short  or  even  too  long  if  it  be  an  endless  belt. 
If  the  machine  has  a  belt-tightener,  measure  for  belt  when 
position  of  tightener  makes  belt  the  shortest,  in  order  to 
allow  for  stretch,  which  is  considerable  in  some  belts. 

Avoid  short  or  vertical  belts,  as  they  are  much  more  apt 
to  slip  than  long  or  horizontal  ones.  If  it  is  absolutely 
necessary  to  connect  pulleys  at  different  levels,  make  the 
belt  as  nearly  horizontal  as  possible.  The  distance  between 
the  centres  of  two  belt-connected  pulleys  should  be  at  least 
three  times  the  diameter  of  the  larger  pulley,  and  it  may 
well  be  four  times  if  the  space  permits. 

Make  belt  just  tight  enough  to  avoid  slipping  without 
straining  the  shaft  or  bearings.  A  new  belt  will  not  carry 
as  much  power  as  one  which  has  been  properly  used  for  a 
few  months. 

The  dynamo  or  motor  shaft  and  the  shaft  to  which  it  is 
to  be  belted  should  be  placed  exactly  parallel  and  the 
centres  of  the  two  pulleys  should  be  exactly  opposite  each 
other  in  a  straight  line  perpendicular  to  the  shafts.  The 
machine  should  then  be  turned  slowly  by  hand  to  see  if  the 
belt  tends  to  run  to  one  side  of  pulley,  in  which  case  the 
machine  should  be  slightly  moved  until  the  belt  runs  in  the 
middle  of  the  pulleys  and  does  not  tend  to  work  to  one 
side. 

Rubber  belt  has  50$  more  adhesion  than  leather.  Eub- 
ber  and  canvas  stretch  continuously.  For  new  leather 
allow  \  inch  per  foot  for  stretching. 

Belts  "  creep "  over  pulley  or  loose  speed  about  2$. 
Hence  in  determining  size  of  pulleys  when  speed  must  be 
accurate,  arrange  them  to  make  speed/^wre  out  2$  too  high. 

Electrical  Connections. — As  already  stated  these  should 
be  very  carefully  cleaned,  and  this  may  well  be  car- 
ried to  the  extent  of  rubbing  them  vigorously  with  clean 


Dynamos  and  Motors.  15 

cloth  or  chamois  skin.  Any  of  the  metal  surfaces  used  in 
making  electrical  contacts  which  are  tarnished  should  be 
brightened  with  fine  sandpaper  or  by  scraping  them,  but 
all  sand,  metallic  particles,  etc.,  must  be  carefully  removed 
afterwards.  Particles  of  sand  or  dirt  are  often  left  acci- 
dentally between  surfaces  which  should  be  in  perfect  con- 
tact. 


*  —  It  is  very  desirable  to  have  a  thoroughly 
competent  lineman  or  electrician  to  connect  a  dynamo  or 
motor  to  the  circuit,  see  that  everything  is  properly  ar- 
ranged and  start  the  machine  the  first  time. 


FIG.  4.— WIRES  CARRIED  ON  PORCELAIN. 

The  connections  should  all  be  made  in  a  substantial  and 
permanent  manner.  Good  quality  of  insulated  wire  should 
be  used  and  should  be  properly  arranged  and  laid. 

Temporary,  loose  or  poorly  insulated  wires  or  connec- 
tions are  very  objectionable.  All  circuits  exposed  to 
moisture  should  be  supported  on  glass,  porcelain  or  other 
waterproof  insulators.  Circuits  of  over  250  volts  even 
where  not  exposed  to  moisture  should  also  preferably  be 
carried  on  porcelain  or  similar  insulators,  as  shown  in  Fig. 
4,  and  out  of  reach  if  possible,  and  the  best  insulated  wire 
should  be  used. 

Low- voltage  circuits  of  230  volts  or  under  may  be  run 
in  wooden  moulding  or  cleats  where  entirely  unexposed  to 


16  Practical  Management  of 

moisture.  Where  wires  pass  through  walls,  floors,  over 
pipes  or  are  otherwise  liable  to  injury  they  should  be  pro- 
tected by  hard-rubber  tubing  or  other  equally  good  cover- 
ing. No  wire  smaller  than  No.  8  B.  &  S.  gauge  should  be 
used  for  the  arc  current  of  10  amperes,  and  other  wires 
should  be  in  proportion;  that  is,  they  should  have  from 
800  to  1,200  circular  mils  per  ampere/  The  former  figure 
(800)  is  for  small  wires,  in  cool  places  ;  the  latter  figure 
(1,200)  is  for  wires  carrying  heavy  currents  or  high  volt- 
age and  wires  in  hot  places  such  as  ceilings  of  kitchens, 
etc.  No  wire  smaller  than  No.  16  should  ever  be  laid  to 


Current  •*  4-  amp.  Cuxrext=JOajnp. 

Resistance  =.&Sohjn  Resistance  *.4-o?i  n 

JJrop  -.2£x  4  =  Ivol  t  Uj-op=.4-xlO=4-.  volts 


115  -  4-  -J= 


32.  c.p    lamps  32c. 


FIG.  5.— "DROP"  ON  BRANCHING  CIRCUITS. 

carry  any  current  from  a  dynamo  (smaller  wires  may  be 
used  for  primary  battery  currents)  no  matter  how  small 
the  current  may  be. 

The  above  sizes  of  wire  are  rather  larger  than  are  gen- 
erally given  but  it  is  wise  to  have  an  ample  margin. 
Failure  to  allow  a  proper  margin  or  factor  of  safety  has 
been  the  cause  of  most  of  the  troubles  in  all  branches  of 
electrical  work. 

In  addition  to  the  above  allowances  for  current  capacity 
or  the  ability  of  wires  to  carry  the  current  without  over- 
heating, it  is  also  necessary  to  consider  the  fall  of  potential 


Dynamos  and  Motors.  17 

or  "  drop  "  on  wires.  This  loss  ought  not  to  exceed  5  per 
cent,  in  isolated  plants,  10  per  cent,  in  central  station  sys- 
tems, and  about  20  per  cent,  in  long-distance  transmission. 
That  is  to  say,  the  voltage  at  the  most  remote  point  on  the 
system  should  not  fall  below  the  voltage  at  the  dynamo  by 


FIG.  6.— DOUBLE-POLE  QUICK-BREAK  SWITCH. 

more  than  these  percentages.  A  "  wiring  table  "  is  given 
at  the  end  of  this  work  for  determining  the  size  of  wire  re- 
quired in  various  cases.  A  simple  rule  derived  from  Ohm's 
law  applicable  to  all  cases  is,  that  the  lost  voltage  obtained 


18 


Practical  Management  of 


by  multiplying  the  current  in  amperes  at  full  load  by  the 
total  resistance  of  the  circuit  in  ohms  must  not  be  more 
than  the  given  percentage  of  the  voltage  at  the  generator. 
In  the  case  of  a  branching  circuit,  shown  in  Fig.  5,  or 
other  case  where  the  current  is  not  the  same  throughout, 
the  separate  parts  should  be  treated  separately  as  indicated 
in  the  diagram.  This  calculation  applies  particularly  to 
motors  which  are  often  put  at  the  end  of  a  long  circuit  or 
branch. 


FIG.  7. — SHUNT  DYNAMO  ON  CONSTANT  POTENTIAL  CIRCUIT 
WITH  LAMPS  IN  PARALLEL. 


Switches  and  Cut-Outs.— The  bases  of  all  switches, 
cut-outs,  etc.,  should  be  of  slate,  porcelain  or  other  fire- 
proof, non-porous,  insulating  material.  On  all  constant- 
potential  or  multiple  arc  circuits,  double-pole  fusible  cut- 
outs should  be  put  where  each  branch  starts.  On  all  con- 
stant-current or  arc  circuits,  double-pole  cut-out  switches 
should  be  put  where  the  circuit  enters  any  building  and 


Dynamos  and  Motors. 


19 


also  near  any  motor  or  group  of  lamps  on  such  circuits. 
All  high-voltage  circuits  and  any  low-voltage  circuit  carry- 
ing more  than  three  amperes  should  be  controlled  by  double- 
pole  switches  or  cut-outs  which  entirely  disconnect  both 
sides  of  the  circuit,  and  they  should  also  preferably  have  a 
*  '  quick  break, "  especially  with  direct  currents. 

The  exceptions  to  this  rule  are,  first,  constant-potential 
dynamos  which  usually  have  single-pole  knife  switches,  the 


FIG.  8.— SERIES  DYNAMO  ON  CONSTANT  CURRENT  CIRCUIT  WITH 
LAMPS  IN  SERIES. 


other  pole  being  permanently  connected  to  the  circuit ;  and 
second,  constant- potential  motors  which  generally  have 
single-pole  switches  on  the  starting  boxes,  the  other  pole 
being  always  connected  to  the  circuit.  In  the  latter  case, 
however,  it  is  recommended  to  also  put  a  double-pole  quick- 
break  switch  in  the  circuit,  as  shown  in  Fig.  6. 


20 


Practical  Management  of 


Diagrams  of  Connections  are  given  in  each  im- 
portant case  to  show  the  actual  connections  which  are 
necessary.  But  when  a  machine  is  to  be  "  connected  up  " 
a  competent  electrical  engineer  should  be  consulted  or 
an  exact  diagram  should  be  obtained  from  the  maker  of 
the  machine,  as  its  connections  may  be  peculiar  and  cause 
serious  trouble.  Diagrams  merely  represent  the  path  of 


Main 


FIG.  9. — ALTERNATING  CURRENT  PLANT. 


the  wires  in  the  simplest  way,  the  important  thing  in  elec- 
trical connections  being  which  parts  or  wires  are  connected, 
not  how  they  are  connected.  Whether  the  path  be  straight 
or  crooked,  vertical  or  horizontal,  etc.,  is  of  no  consequence. 
Diagrams  of  the  three  most  important  cases  of  dynamo 
connections  are  here  given.  The  other  diagrams  of 
dynamos  and  motor  connections  are  given  hereafter. 


Dynamos  and  Motors.  21 

Shunt  Dynamo  on  Constant-Potential 
Circuit  is  represented  in  Fig.  7  with  the  necessary  con- 
nections. The  brushes  B  and  B  are  connected  to  the  two 
conductors  forming  the  main  circuit,  also  to  the  field  mag- 
net coils  through  a  resistance  box  to  regulate  the  strength 
of  current  and  therefore  the  magnetism  in  the  field.  A  volt- 
meter is  also  connected  to  the  two  brushes  or  main  con- 
ductors to  measure  the  voltage  or  electrical  pressure  be- 
tween them.  One  of  the  main  conductors  is  connected  to 
an  amperemeter  which  measures  the  total  current  on  the 
main  circuit.  The  lamps  are  connected  in  parallel  between 
the  main  conductors  or  branches  from  them. 

Series  Dynamo  on  Constant-Current 
Circuit. — The  connections  in  this  case  (Fig.  8)  are 
extremely  simple,  the  armature,  field  coils,  amperemeter, 
main  circuit  and  lamps,  all  being  connected  in  one  series. 

Alternating -Cur  rent  Plant.— The  proper  con- 
nections in  this  case  are  shown  in  Fig.  9,  in  which  the 
names  of  the  different  parts  of  the  plant  are  given  and 
which  therefore  requires  no  explanation. 

The  diagrams  of  connections  of  all  cases  of  dynamos 
coupled  together  and  of  electric  motors  are  given  in  the 
chapter  on  Starting  where  they  are  required  to  explain  the 
proper  steps. 


22  Practical  Management  of 


CHAPTER  IV. 

DIRECTIONS    FOR    STARTING    DYNAMOS    AND    MOTORS. 

General. — Make  sure  that  the  machine  is  clean 
throughout,  especially  the  commutator,  brushes,  electrical 
connections,  etc.  Remove  any  metal  dust,  as  it  is  very 
likely  to  make  a  ground  or  short-circuit. 

Examine  the  entire  machine  carefully  and  see  that  there 
are  no  screws  or  other  parts  that  are  loose  or  out  of  place. 
See  that  the  oil  cups  have  a  sufficient  supply  of  oil,  and 
that  the  passages  for  the  oil  are  clean  and  the  feed  is  at 
the  proper  rate.  In  the  case  of  self-oiling  bearings  see 
that  the  rings  or  other  means  for  carrying  the  oil  work 
freely.  See  that  the  belt  is  in  place  and  has  the  proper 
tension.  If  it  is  the  first  time  the  machine  is  started  it 
should  be  turned  a  few  times  by  hand,  or  very  slowly,  in 
order  to  see  if  the  shaft  revolves  easily  and  belt  runs  in 
centres  of  pulleys. 

The  brushes  should  now  be  carefully  examined  and  ad- 
justed to  make  good  contact  with  the  commutator  and  at 
the  proper  point,  the  switches  connecting  the  machine 
to  the  circuit  being  left  open.  The  machine  should  then 
be  started  with  care  and  brought  up  to  full  speed  gradu- 
ally if  possible,  and  in  any  case  the  person  who  starts 
either  a  dynamo  or  motor  should  closely  watch  the  ma- 
chine and  everything  connected  with  it  and  be  ready  to  in- 
stantly shut  down  and  stop  it  (and  throw  it  out  of  circuit 
if  it  is  connected)  if  the  least  thing  seems  to  be  wrong, 
and  should  then  be  sure  to  find  out  and  correct  the  trouble 
before  starting  again.  (See  "  Locating  and  Remedying 
Troubles.") 


Dynamos  and  Motors.  23 

Starting  a  Dynamo.— In  the  case  of  a  dynamo 
it  is  usually 'brought  up  to  speed  either  by  starting  up  a 
steam  engine  or  by  connecting  the  dynamo  to  a  source  of 
power  already  in  motion.  The  former  should  of  course 
only  be  attempted  by  a  person  competent  to  manage  steam 
engines  and  familiar  with  the  particular  type  in  question. 
This  requires  special  knowledge  acquired  by  experience,  as 
there  are  many  points  to  appreciate  and  attend  to,  the  ne- 
glect of  any  of  which  might  cause  serious  trouble.  For 
example,  the  presence  of  water  in  the  cylinder  might 
knock  out  the  cylinder  head;  the  failure  to  properly  set  the 
feed  of  the  oil  cups  might  cause  the  piston  rod,  shaft  or 
other  part  to  cut,  or  other  great  or  small  damage  might 
be  done  by  ignorance  or  carelessness.  The  mere  mechani- 
cal connecting  of  a  dynamo  to  a  source  of  power  is  usu- 
ally not  very  difficult;  nevertheless,  it  should  be  done  care- 
fully and  intelligently,  even  if  it  only  requires  throwing  in 
a  friction  clutch  or  shifting  a  belt  from  a  loose  pulley.  To 
put  a  belt  on  a  pulley  in  motion  is  difficult  and  dangerous, 
particularly  if  the  belt  is  large  or  the  speed  is  high,  and 
should  not  be  tried  except  by  a  person  who  knows  just  how 
to  do  it.  Even  if  a  stick  is  used  for  this  purpose  it  is  apt 
to  be  caught  and  thrown  around  by  the  machinery  unless 
it  is  used  in  exactly  the  right  way. 

It  has  been  customary  to  bring  dynamos  to  full  speed 
before  the  brushes  are  lowered  into  contact  with  the  com- 
mutator, but  there  is  no  particular  reason  for  this  practice, 
provided  the  dynamo  is  not  allowed  to  turn  backwards, 
which  sometimes  occurs  from  carelessness  in  starting,  and 
might  injure  copper  brushes  by  causing  them  to  catch  in 
the  commutator.  If  the  brushes  are  put  in  contact  before 
starting  they  can  be  more  easily  and  perfectly  adjusted, 
and  the  E.  M.  F.  comes  up  slowly  so  that  any  fault  or  diffi- 
culty will  develop  gradually  and  can  be  corrected,  or  the 
machine  stopped,  before  any  injury  is  done  to  it  or  to  the 
system.  In  fact,  if  the  machine  is  working  alone  on  a  sys- 
tem and  is  absolutely  free  from  any  danger  of  short-cir- 


24  Practical  Management  of 

cuiting  any  other  machine  or  storage  battery  on  the  same 
circuit,  it  may  be  started  up  connected  to  the  circuit,  in 
which  case  the  E.  M.  F.  and  current  feel  their  way,  so 
to  speak,  through  the  whole  system,  and  any  trouble  mani- 
fests itself  so  slowly  that  it  can  be  taken  care  of  before 
serious  injury  results. 

If,  however,  a  dynamo  is  to  be  connected  to  another  or 
to  a  circuit  having  other  dynamos  or  a  storage  battery 
working  upon  it,  the  greatest  care  should  be  taken.  In  fact, 
this  coupling  together  of  dynamos  can  be  done  perfectly 
if  exactly  the  correct  method  is  followed,  but  is  likely  to 
cause  serious  trouble  if  any  mistake  is  made. 

Coupling  Dynamos. — Two  or  more  machines 
are  often  connected  to  a  common  circuit.  This  is  especially 
the  case  in  electric  lighting  where  the  number  of  lamps 
required  to  be  fed  varies  so  much  that  one  dynamo  may 
be  sufficient  for  certain  hours,  but  two,  three  or  more 
machines  may  be  required  at  other  times. 

Dynamos  may  be  connected  together  either  in  parallel 
(multiple  arc)  or  in  series. 

Dynamos  in  Parallel. — In  this  case  the  -+-  ter- 
minals are  connected  together  or  to  the  same  line  and  the 
—  terminals  are  connected  together  or  to  the  other  line. 
The  currents  (i.  e.9  amperes)  of  the  machines  are  thereby 
added  but  the  E.  M.  P.  (volts)  are  not  increased.  The 
chief  condition  for  the  running  of  dynamos  in  parallel  is 
that  their  voltages  should  be  equal  but  their  current 
capacities  may  be  different.  For  example:  A  dynamo  pro- 
ducing 10  amperes  may  be  connected  to  another  generating 
100  amperes,  provided  the  voltages  agree.  Parallel  work- 
ing is  therefore  suited  to  constant  potential  circuits.  A 
dynamo  to  be  connected  in  parallel  with  others  or  with  a 
storage  battery  must  first  be  brought  up  to  its  proper 
E.  M.  F.  speed  and  other  working  conditions,  otherwise 
it  will  short-circuit  the  system,  and  probably  burn  out 
its  armature.  Its  field  magnetism  must  also  be  at  full 


Dynamos  and  Motors. 


25 


strength  owing  to  the  fact  that  it  generates  no  E.  M.  F.  with 
no  field  magnetism.  Hence  it  is  well  to  find  whether  the 
pole- pieces  are  strongly  magnetized  by  testing  them  with 
a  piece  of  iron,  and  make  sure  of  the  proper  working  of 
the  machine  in  all  other  respects  before  connecting  the 
armature  to  the  circuit.  It  is  quite  c  >mmon  for  the  field 
circuit  to  be  open  at  some  point  and  thus  cause  very 
serious  results.  In  fact,  a  dynamo  should  not  be  connected 
to  a  circuit  in  parallel  with  others  until  its  voltage  has  been 


Field  Jtefttlalor 


FIG.  10.— SHUNT  DYNAMOS  IN  PARALLEL. 

tested  and  found  to  be  equal  to  or  slightly  (not  over  1  or  2 
per  cent.)  greater  than  that  of  the  circuit.  This  test  may 
be  made  by  first  measuring  the  E.  M.  F.  of  the  circuit  and 
then  of  the  machine  by  one  voltmeter  ;  or  voltmeters  con- 
nected to  each  may  be  compared.  Another  method  is  to 
connect  the  dynamo  to  the  circuit  through  a  high  resistance 
and  a  galvanometer,  and  when  the  latter  indicates  no  cur- 
rent it  shows  that  the  voltage  of  the  dynamo  is  equal  to 
that  of  the  circuit.  A  rougher  and  simpler  way  to  do  this 
is  to  raise  the  voltage  of  the  dynamo  until  its  "  pilot 


26  Practical  Management  of 

lamp,"  or  other  lamp  fed  by  it,  is  fully  as  bright  as  the 
lamps  on  the  circuit,  and  then  connect  the  dynamo  to  the 
circuit.  Of  course  the  lamps  compared  should  be  intended 
for  the  same  voltage  and  in  normal  condition.  Be  sure  to 
connect  the  -\-  terminal  of  the  dynamo  to  the  +  wire  and 
the  —  terminal  to  the  —  wire,  otherwise  there  will  be  a 
very  bad  short-circuit. 

When  the  dynamo  is  first  connected  in  this  way  it  should 
only  supply  a  small  amount  of  current  to  the  circuit  (as 
indicated  by  its  ammeter)  and  its  voltage  should  then  be 


FIG.  11.— SERIES  DYNAMOS  IN  PARALLEL.— MUTUAL  ACTION. 


gradually  raised  until  it  generates  its  proper  share  of  the 
total  current. 

If  the  voltage  of  the  dynamo  is  less  than  that  of  the  cir- 
cuit, the  current  will  flow  back  into  the  dynamo  and  cause 
it  to  be  run  as  a  motor.  If  it  is  shunt  wound  the  direction 
of  rotation  is  the  same,  however,  and  no  great  harm  results 
with  a  slight  difference  in  voltage.  Shunt  machines  are 
therefore  particularly  suited  to  being  run  in  parallel,  Fig.  10. 

Series   Wound   Dynamos   in   Parallel. — If 

the  machine  is  series  wound,  this  back  current  would  cause 


Dynamos  and  Motors. 


27 


a  reversal  of  field  magnetism,  and  motion  which  is  very 
objectionable.  In  fact,  series  dynamos  in  parallel  are  in 
very  unstable  equilibrium,  because  if  either  tends  to  gen- 
erate too  little  current  that  very  fact  weakens  its  own  field 
which  is  in  series,  and  thus  still  further  reduces  its  current 
and  probably  reverses  it.  One  way  to  run  series  dynamos 
in  parallel  is  to  cause  each  to  excite  the  other's  field  magnet, 
as  shown  in  Fig.  11,  whereby  if  one  generates  too  much  cur- 
rent it  strengthens  the  field  of  the  other  and  counteracts 
itself,  so  to  speak. 


FIG.  12.— SERIES  DYNAMOS  IN  PARALLEL.— EQUALIZING  WIRE. 

The  other  way,  Fig.  12,  to  run  series  dynamos  in  paral- 
lel, is  to  connect  together  the  two  ••{-  brushes  by  what  is 
called  an  "  equalizer,"  as  well  as  the  two  —  brushes.  By 
this  means  the  electrical  pressure  at  the  terminals  of  the 
two  armatures  is  made  the  same,  and  the  currents  in  the 
two  fields  are  also  made  equal.  Series  machines  are  not 
often  run  in  parallel,  but  the  principles  just  explained  help 
the  understanding  of  the  next  case,  which  is  important. 

Compound  Dynamos  in  Parallel.— Since  the 

field  magnets   of   these   machines  are  wound    with    series 


28  Practical  Management  of 

coils  as  well  as  shunt,  the  coupling  of  them  is  a  combina- 
tion of  the  cases  of  the  shunt  and  the  series  wound  machines 
just  described. 

Fig.  13  represents  two  compound  machines  in  parallel. 

Assume  that  one  machine  is  already  running,  that 
switches  F1  in  the  shunt  circuit  and  s1  in  the  main  circuit 
are  closed,  and  that  armature  No.  1  is  generating  its  full 
current  and  feeding  the  lamps  on  the  main  circuit,  the 
shunt  and  series  field  coils  of  the  machine  carrying  their 
proper  current.  Now  to  throw  on  the  other  dynamo,  its 
armature  No.  2  is  brought  up  to  normal  speed,  switch  F2 
is  closed,  which  excites  its  shunt  coil.  Switch  E,  on  the 
"  equalizer "  is  then  closed,  which  excites  its  series  coil 
with  part  of  the  main  current  from  No.  1.  The  second 
machine  then  gives  its  full  voltage,  and  its  main  switch  s2 
to  make  it  produce  its  share  of  the  current  for  the  main 
is  then  closed  and  the  voltage  of  the  machine  is  regulated 
circuit.  It  would  be  well  to  actually  compare  the  voltage 
before  closing  the  main  switch,  as  just  described  for  shunt 
machines,  making  the  voltage  equal  at  first,  so  that  the 
machine  generates  little  or  no  current,  and  then  raise  it  till 
the  machine  does  its  share  of  the  work. 

In  disconnecting  a  machine  the  same  steps  are  taken, 
only  exactly  in  the  reverse  order.  More  than  two  com- 
pound machines  may  be  run  in  parallel  in  this  way  by  con- 
necting them  in  a  precisely  similar  manner. 

Compound  dynamos  of  different  size  or  current  capacity 
may  also  be  coupled  in  this  way,  provided  of  course  their 
voltages  are  equal,  and  provided  also  that  the  resistances 
of  the  series  field  coils  are  inversely  proportional  to  the 
current  capacities  of  the  several  machines,  that  is,  if  a  dy- 
namo produces  twice  as  much  current  its  series  coil  should 
have  half  the  resistance. 

The  switch  E  is  often  left  closed  all  the  time,  in  fact,  a  per- 
manent "  equalizing, "  connection  may  be  made  between 
the  corresponding  brushes  of  two  or  more  machines.  This 
has  the  effect  of  "compounding"  the  dynamos  collectively 


Dynamos  and  Motors.  29 

instead  of  individually.  For  example,  when  only  one  dy- 
namo is  working,  its  current  divides  among  the  series  coils 
of  all  and  these  coils  will  not  be  highly  excited,  when 
however  all  the  dynamos  are  working  the  whole  current 
of  each  will  pass  through  its  series  coil.  Thus  the  greatest 
field  strength  and  therefore  voltage  is  produced  when 


FIG.  13.— COMPOUND  DYNAMOS  IN  PARALLEL. 

most  needed — at  full  load.  The  equalizing  conductor 
should  be  able  to  carry  at  least  half  the  full  current  of  one 
dynamo.  This  method  of  running  compound  dynamos  in 
parallel  is  important  because  it  makes  the  effect  of  the 
series  coil  proportional  to  the  total  load,  not  to  the  load  on 
each  machine.  This  is  particularly  desirable  in  central 


30  Practical  Management  of 

stations  or  where  the  dynamos  are  "overcompounded." 
Compound  dynamos  run  in  parallel  in  this  way,  as 
well  as  shunt  machines,  tend  to  steady  each  other,  for  if 
one  happens  to  run  too  fast,  it  has  to  do  more  work  which 
opposes  the  increase  of  speed,  and  it  also  takes  part  of  the 
load  off  the  other  machines  which  will  therefore  tend  to 
run  faster,  thus  producing  equality.  This  mutual  regula- 
tion will  take  care  of  any  slight  difference  between  ma- 
chines such  as  the  slip  of  belt,  but  the  difference  must  not 
be  great. 

Alternators  in  Parallel. — Since  the  alternating 
current  consists  of  waves,  it  is  necessary,  in  order  to  prop- 
erly connect  alternators  together,  that  they  should  agree 
in  two  respects — first,  in  frequency  or  the  number  of 
waves  produced  per  second,  and  second  in  phase,  that  is, 
they  should  be  at  corresponding  points  of  the  current 
waves  at  the  same  instant.  The  case  is  precisely  similar 
to  that  of  two  persons  walking  together,  they  should  not 
only  have  the  same  rate  but  they  should  also  be  in  step. 
If  an  alternator  is  thrown  into  circuit  with  others  when 
not  in  phase  it  will  cause  several  severe  fluctuations  in  the 
lamps,  and  then  the  machines  will  bring  e^ch  other  into 
unison  since  they  exert  a  mutual  control  on  each  other, 
similar  to  that  just  described  in  the  case  of  compound  ma- 
chines, only  much  stronger.  In  fact,  an  alternator  resists 
being  thrown  out  of  step  with  others  by  an  amount  equal 
to  the  full  torque  or  pull  required  to  drive  it. 

Therefore  to  thro  wan  alternator  into  circuit  with  others, 
bring  its  speed  up  to  the  proper  point,  regulate  the  field 
exciting  current  to  make  the  voltage  of  the  machine  equal 
to  that  of  the  circuit. 

The  phase  may  then  be  determined  by  connecting  one 
lamp  to  the  secondary  circuits  of  two  transformers  at  the 
same  time,  one  in  circuit  with  the  machine  to  be  switched 
in  and  the  other  on  the  main  circuit.  The  secondaries  of, 
say,  50  volts  each  should  be  connected  in  series  with  each 
other  and  to  a  100-volt  lamp.  When  the  machines  are 


Dynamos  and  Motors. 


31 


opposed  the  lamp  is  dim,  and  vice  versa.  If  the  lamp  flickers 
badly  the  phase  is  not  right,  but  if  the  lamp  is  steady  the 
machine  is  in  phase  and  it  may  be  connected  by  closing  its 
main  switch  without  disturbing  the  circuit.  If  dynamos 
are  rigidly  connected  to  each  other  or  to  the  engine  so 
that  they  necessarily  run  exactly  together,  there  is  no  need 
of  bringing  them  into  step  each  time,  but  they  should  be 
adjusted  to  the  same  phase  in  the  first  place. 

Dynamos  in  Series. — This  arrangement  is  much 
less  common  than   parallel  working  and  does  not  usually 


FIG.  14.— SHUNT  DYNAMOS  IN  SERIES. 


operate  so  well.     The  conditions  are  exactly  opposite  in 
the  two  cases. 

To  connect  machines  in  series  the  -j-  terminal  of  one 
must  of  course  be  connected  to  the  —  terminal  of  the  next 
and  so  on.  If  dynamos  are  in  series  each  of  them  must 
have  a  current  capacity  equal  to  the  maximum  current  on 
the  circuit,  but  they  may  differ  to  any  extent  in  E.  M.  F. 
The  voltages  of  machines  in  series  are  added  together,  and 
therefore  danger  to  persons,  insulation,  etc.,  is  increased 
in  proportion. 


32 


Practical  Management  of 


Shunt  or  Compound  Dynamos    in  Series 

may  be  run  well,  provided  the  shunt  field  coils  are  connected 
together  to  form  one  shunt  across  both  machines  as  in- 
dicated in  Fig.  14. 

Series  Wound   Dynamos  in  Series  may  be 

connected  in  the  simple  way  represented  in  Fig.  15,  but 
usually  machines  are  connected  in  series  for  arc  lighting 
when,  for  example,  two  forty-light  dynamos  are  run  on 


FIG.  15.— SERIES  WOUND  DYNAMOS  IN  SERIES. 


one  circuit  of  eighty  lamps,  in  which  case  the  dynamos 
usually  have  some  form  of  regulator.  These  regulators  do 
not  work  well  together  because  they  are  apt  to  " see-saw" 
with  each  other.  This  difficulty  may  be  overcome  either 
by  connecting  the  regulators  so  that  they  will  work  together 
or  by  setting  one  regulator  to  give  full  E.  M.  F.  and  let 
the  other  alone  control  the  current.  This  latter  plan  can 
only  be  followed  when  the  variation  in  load  does  not 
exceed  the  power  of  one  machine. 


Dynamos  and  Motors. 


33 


Alternators  in  Series.  —  The  same  mutual  regu- 
lating tendency  which  makes  alternators  run  well  in  par- 
allel causes  them  to  get  out  of  step  and  become  opposed  to 
each  other  in  series.  It  is  impracticable  to  run  them  in 
series  unless  they  are  rigidly  connected  to  run  exactly  in 
phase  so  that  they  add  their  waves  of  current  instead  of 
counteracting  each  other.  This  is  a  case  that  rarely 
arises  in  practice. 


,    \  220 

T    (VoUs 


FIG.  16.— THREE- WIRE  SYSTEM. 


Dynamos  on  the  Three-Wire  System  (Di- 
rect Current).-^ln  the  ordinary  three-wire  system  for 
incandescent  lighting  as  represented  in  Fig.  16,  no  par- 
ticular precautions  are  required  in  starting  or  connecting 
dynamos.  As  a  matter  of  fact  the  two  dynamos  are  in- 
dependent of  each  other  and  work  on  practically  separate 
circuits.  Dynamo  1  feeds  the  circuit  formed  by  the 
mains  marked  -f-  and  N,  and  dynamo  2  feeds  the  circuit 
formed  by  mains  N  and — .  The  "  neutral "  wire  N  merely 


34  Practical  Management  of 

acts  as  a  common  conductor  for  both  circuits.  The  E.  M. 
F.  on  each  of  these  circuits  should  of  course  be  kept  con- 
stant at  the  prescribed  voltage  and  therefore  equal.  The 
current  on  the  two  circuits  or  "sides"  of  the  system  as 
they  are  called,  should  be  kept  as  nearly  equal  as  possible 
by  distributing  the  lamps  equally  between  them.  Any 
difference  in  current  either  way  is  carried  by  N.  One  dy- 
namo may  be  run  alone  on  one  side  of  the  system  and  the 
only  effect  of  throwing  on  the  other  dynamo  is  to  reduce 
the  "  drop  "  or  fall  of  potential  on  the  wire  N.  In  fact  if 
the  load  is  equal  on  both  sides  there  is  practically  no  cur- 
rent or  drop  in  N.  If  dynamos  are  put  on  the  circuit  in 
parallel  also  —  for  example,  two  in  parallel  on  each  side  of 
the  system,  making  four  dynamos  in  all,  then  the  machines 
on  each  side  are  managed  simply  as  dynamos  in  parallel, 
as  previously  described.  In  starting  up  dynamos  on  the 
three-wire  system,  it  is  better  to  start  one  machine  at  a 
time  and  get  that  working  properly  as  already  described, 
and  then  put  on  a  machine  on  the  other  side  of  the  system 
to  keep  the  two  sides  even.  The  addition  of  dynamos  in 
parallel  on  each  side  should  also  be  done  singly  just  as  on  a 
simple  two-  wire  circuit. 


Motors.  —  The  general  instructions  relat- 
ing to  adjustment  of  brushes,  screws,  belt,  oil  cups,  etc., 
given  in  the  beginning  of  this  chapter  should  be  carefully 
followed  preparatory  to  starting  a  motor. 

The  actual  starting  of  a  motor  is  usually  a  simple  matter 
since  it  consists  merely  in  operating  a  switch,  but  in  each 
case  there  are  one  or  more  important  points  to  consider. 

Constant  Potential  Motor  (Shunt  Wound).  —  A 
motor,  to  run  at  constant  speed  on  a  constant  potential  cir- 
cuit (a  110-volt  incandescent  lighting  circuit,  for  example), 
is  usually  plain  shunt  wound.  This  is  the  commonest  form 
of  stationary  motor.  The  field  coils  are  wound  with  the 
right  size  of  wire  to  take  the  proper  magnetizing  current 
as  in  the  case  of  a  shunt  dynamo,  and,  since  the  potential 


Dynamos  and  Motors. 


35 


is  constant,  the  field  strength  is  constant.  Shunt  coils 
must  not  be  used  however  if  the  potential  is  more  than  5 
per  cent,  higher,  or  20  per  cent,  lower,  than  that  for  which 
they  are  intended,  as  stated  elsewhere. 


fatt-OUf 


FIG.  17.— SHUNT  MOTOR  ON  CONSTANT  POTENTIAL  CIRCUIT. 

Throwing  the  field  into  circuit  is  therefore  simple,  but 
the  current  in  the  armature  in  starting  is  quite  difficult  to 
take  care  of,  because  the  resistance  of  the  armature. is  very 
low  in  order  to  get  high  efficiency  and  constancy  of  speed, 


86  Practical  Management  of 

and  the  rush  of  current  through  it  in  starting  might  be 
ten  or  more  times  the  normal  number  of  amperes.  To  pre- 
vent this  excessive  current,  motors  are  started  on  constant 
potential  circuits  through  a  rheostat  or  "starting  box," 
containing  resistance  coils  as  represented  in  Fig.  1 7.  The 
main  wires  are  connected  through  a  branch  cut-out  (with 
safety  fuses)  and  preferably  also  a  double-pole  quick-break 
switch  Q,  to  the  motor  and  box  as  indicated.  When  the 
switch  Q  is  closed  and  the  arm  s  is  turned  to  the  right,  the 
field  circuit  is  closed  through  the  contact  strip  F  and  the 
armature  circuit  is  closed  through  the  resistance  coils  a,  a, 
a  which  prevent  the  rush  of  current  referred  to.  The 
motor  then  starts  and  as  its  speed  rises,  it  generates  a 
counter  E.  M.  F.  so  that  the  arm  s  can  be  turned  further 
until  all  the  resistance  coils  a,  a,  a,  are  cut  out  and  the 
motor  is  directly  connected  to  the  circuit  and  running  at 
full  speed.  The  arm  s  should  be  turned  slowly  enough  to 
allow  the  speed  and  counter  E.  M.  F.  to  come  up  as  the 
resistances  a,  a,  a  are  cut  out.  The  arm  s  should  positively 
close  the  field  circuit  first  so  that  the  magnetism  reaches 
its  full  strength  (which  takes  several  seconds)  before  the 
armature  is  connected. 

The  object  of  the  resistance  f  is  explained  under  "  Stop- 
ping Motors."  The  coils  a,  a,  a,  are  made  of  fine  wire 
which  can  only  carry  the  current  for  a  few  seconds  in  a 
"starting  box";  but  if  the  wire  is  large  enough  to  carry 
the  full  current  continuously  it  is  called  a  "  regulator  "  or 
rheostat  because  the  arm  s  may  be  placed  so  that  some  of 
the  resistances  a,  a,  a,  remain  in  circuit  and  they  will  have 
the  effect  of  reducing  the  speed  of  the  motor. 

Constant  Potential  Motor  (Series  Wound).— 
The  ordinary  electric  railway  motor  in  the  500-volt  trolley 
system  is  the  chief  example  of  this  class.  Motors  for  elec- 
tric elevators  and  hoists  are  either  of  this  kind  or  the 
previous  one.  A  similar  rush  of  current  tends  to  occur 
when  this  type  of  motor  is  started  as  in  the  case  just 
described,  but  it  is  somewhat  less  because  the  field  coils 


Dynamos  and  Motors. 


37 


are  in  series  and  their  resistance  reduces  the  excess.  The 
essential  connections  in  this  case  as  indicated  in  Fig.  18, 
are  very  simple,  the  armature,  field  coils  F  F,  and  rheostat, 
all  being  in  series  and  carrying  the  same  current.  The 
series  wound  motor  on  a  constant  potential  circuit  does  not 
have  a  constant  field  strength  and  does  not  tend  to  run  at 
constant  speed  like  a  shunt  motor.  In  fact  it  will  "race  " 
and  tear  itself  apart  if  the  load  is  taken  off  entirely,  it  is 
therefore  only  suited  to  railway,  pump,  fan  or  other  work 


FIG,  18. 


where  variable  speed  is  desired  and  where  there  is  no  dan- 
ger of  the  load  being  removed  or  a  belt  slipping  off. 

Constant  Potential  Motor  (Differentially 
Wound). — This  is  a  shunt  wound  motor  with  the  addition 
of  a  coil  of  large  wire  on  the  field  and  connected  in  series 
with  the  armature  in  such  a  way  as  to  oppose  the  magnet- 
izing effect  of  the  shunt  winding. 

It  was  formerly  much  used  to  obtain  very  constant 
speed,  but  it  has  been  found  that  a  plain  shunt  motor  is 


38  Practical  Management  of 

sufficiently  constant  for  almost  all  cases.  The  differential 
motor  has  the  great  di>  advantage  that,  if  overloaded,  the 
current  in  the  opposing  (series)  field  coil  becomes  so  great 
as  to  kill  the  field  magnetism  and  the  armature  slows 
down  or  stops  and  is  liable  to  burn  out ;  whereas  a 
plain  shunt  motor  can  increase  its  power  greatly  for  a 
minute  or  so  when  overloaded  and  will  probably  throw 
off  the  belt  or  carry  the  load  until  it  decreases  to  the  normal 
amount. 

Constant  Current  Motor. — The  commonest  ex- 
ample is  a  series  wound  motor  on  the  arc  circuit.  The 
connections  are  shown  in  Fig.  19.  The  switch  1  is  to  en- 
tirely disconnect  the  circuit  from  the  building  in  case  of  fire 
or  other  emergency.  By  simply  turning  the  other  switch  2 
the  motor  is  started  or  stopped,  and  since  the  current  is 
constant  the  motor  may  be  overloaded  or  held  still  without 
injury,  whereas  a  constant  potential  motor  would  burn  out. 

The  precaution  necessary  is  never  to  touch  the  machine 
with  current  on,  as  the  E.  M.  P.  is  probably  high  and  very 
dangerous.  Turn  off  the  switch  to  fix  the  machine.  A 
constant  current  motor  should  be  provided  with  an  effective 
centrifugal  governor  for  controlling  the  speed,  otherwise 
it  will  run  away  when  the  load  is  taken  off,  like  a  series 
motor  on  a  constant  potential  circuit. 

Alternating  Current  Motors.— These  have  not 
been  very  extensively  used  up  to  the  present  time,  al- 
though a  great  variety  of  forms  have  been  tried  or  sug- 
gested. Alternating  motors  are  required  to  run  on  constant 
potential  circuits  since  almost  all  alternating  current 
systems  are  of  this  kind.  But  with  alternating  current 
there  is  no  trouble  from  the  rush  of  current  which  tends  to 
occur  in  starting  a  motor  with  a  constant  potential  direct 
current,  because  the  self-induction  of  the  field  and  armature 
coils  prevents  it.  There  are  several  types  of  alternating 
current  motors.  The  simplest  of  these  is  a  plain  series  or 
shunt  machine  the  same  as  for  direct  current,  except  that 


Dynamos  and  Motors. 


39 


the  field  magnet  is  laminated  as  well  as  the  armature.  The 
trouble  with  this  type,  which  has  been  used  commercially  in 
small  sizes,  is  that  bad  sparking  is  apt  to  occur  when  the 
brush  passes  from  one  commutator  bar  to  the  next  and 
short-circuits  a  coil  which  has  alternating  currents  gener- 


FIG.  19.— SERIES  MOTOR  ON  CONSTANT  CURRENT  CIRCUIT. 

ated  in  it  by  the  reversals  of  the  field  magnetism.  An  ordi- 
nary alternating  current  dynamo  can  be  used  as  a  motor 
but  its  speed  must  be  brought  to  agree  with  the  current 
alternations  before  it  will  run,  and  then  if  it  loses  this 
exact  speed  it  stop8>  and  is  therefore  unpractical.  In  the 


40  Practical  Management  of 

Tesla  and  other  similar  motors  the  effect  is  obtained  by  a 
rotary  current,  but  this  requires  two  or  more  currents  of 
different  phase  and  usually  a  special  three-wire  system 
would  have  to  be  put  in  before  such  motors  could  be 
operated. 


Dynamos  and  Motors.  41 

CHAPTER  V. 

DIRECTIONS   FOB    RUNNING    DYNAMOS    AND    MOTORS. 

After  one  of  these  machines  has  been  properly  started  as 
described  in  the  previous  chapter,  it  usually  requires  very 
little  attention  while  running,  in  fact  a  dynamo  or  motor 
frequently  runs  well  all  day  without  any  care  whatever. 

In  the  case  of  a  machine  which  has  not  been  run  before 
or  has  been  changed  in  any  way,  it  is  of  course  wise  to 
watch  it  closely  at  first.  It  is  also  well  to  give  the  bear- 
ings of  a  new  machine  plenty  of  oil  at  first,  but  not  enough 
to  run  on  the  armature,  commutator  or  any  part  that  would 
be  injured  by  it,  and  to  run  the  belt  rather  slack  until  the 
bearings  and  belt  have  gotten  into  easy  working  condition. 
If  possible,  a  new  machine  should  be  run  without  load  or 
with  a  light  one  for  an  hour  or  two,  or  several  hours  in  the 
case  of  a  large  machine,  and  it  is  always  very  objection- 
able to  start  a  new  machine  on  full  load. 

This  is  true  even  if  the  machine  has  been  fully  tested  by 
its  manufacturer  and  is  in  perfect  condition,  because  there 
may  be  some  fault  in  setting  it  up  or  other  circumstance 
which  would  cause  trouble.  All  machinery  requires  some 
adjustment  and  care  for  a  certain  time  to  get  it  into  smooth 
working  order. 

When  this  condition  is  reached  the  only  attention  re- 
quired is  to  supply  oil  when  needed,  and  see  that  the 
machine  is  not  overloaded.  The  person  in  charge  should 
always  be  ready  and  sure  to  detect  any  trouble  such  as 
sparking,  the  heating  of  any  part  of  machine,  noise,  ab- 
normally high  or  low  speed,  before  any  injury  is  caused 
and  to  overcome  it  by  following  the  directions  given  in  the 
chapter  devoted  to  these  troubles.  Those  directions  should 


42  Practical  Management  of 

be  pretty  thoroughly  committed  to  mind  in  order  to  facili- 
tate the  prompt  detection  and  remedy  of  any  trouble  when 
it  suddenly  occurs  as  is  apt  to  be  the  case.  If  possible  the 
machine  should  be  shut  down  instantly  when  any  trouble 
or  indication  of  one  appears,  in  order  to  avoid  injury  and 
give  time  for  examination. 

Keep  ail  tools  or  pieces  of  iron  or  steel  away  from  the 
machine  while  running,  as  they  might  be  drawn  in  by  the 
magnetism  and  perhaps  get  between  the  armature  and 
pole-pieces  and  ruin  the  machine.  For  this  reason  use  a 
zinc,  brass  or  copper  oil-can  instead  of  iron  or  "tin" 
(which  last  is  merely  iron  coated  with  tin). 


EIG.  20.— TOOL  INSULATED  WITH  RUBBER  TAPE  OR  TUBING. 

Never  lift  a  commutator  brush  while  machine  is  running 
as  it  might  make  a  bad  burnt  spot,  unless  there  is  one  or 
more  other  brushes  on  the  same  side  to  carry  the  current. 

Touch  the  bearings  and  field  coils  occasionally  to  see 
that  they  are  not  hot.  To  determine  whether  the  arma- 
ture is  running  hot,  place  the  hand  in  the  current  of  air 
thrown  out  from  the  armature  by  centrifugal  force. 

Personal  Safety. — Never  close  a  circuit  through  the 
body.  An  accidental  contact  may  be  made  through  the 
feet,  hands,  knees,  or  other  part  of  body  in  some  peculiar 
and  unexpected  manner.  For  example,  men  have  been 
killed  because  they  were  sitting  on  a  conducting  body. 


Dynamos  and  Motors.  43 

Rubber  gloves  or  rubber  shoes,  or  both,  should  be  used 
in  handling  circuits  over  500  volts.  The  safest  plan  is  not 
to  touch  any  conductor  while  the  current  is  on,  and  it 
should  be  remembered  that  the  current  may  be  present 
when  not  expected,  due  to  an  accidental  contact  with  some 
other  wire  or  a  change  of  connections.  Tools  with  insu- 
lated handles,  Fig.  20,  or  a  dry  stick  of  wood  should  be 
used  instead  of  the  bare  hand. 

The  rule  to  use  only  one  hand  when  handling  dangerous 
electrical  conductors  or  apparatus,  is  a  very  good  one, 
because  it  avoids  the  chance,  which  is  very  great,  of  mak- 
ing contacts  with  both  hands  and  getting  the  full  current 
right  through  the  body.  This  rule  is  often  made  still  more 
definite  by  saying,  "  Keep  one  hand  in  the  pocket "  in  order 
to  make  sure  not  to  use  it.  The  above  precautions  are  often 
totally  disregarded,  particularly  by  those  who  have  become 
careless  by  familiarity  with  dangerous  currents.  The 
result  of  this  has  been  that  almost  all  the  persons  acci- 
dentally killed  by  electricity  have  been  experienced  elec- 
tric linemen. or  station  men. 


44  Practical  Management  of 


CHAPTER  VI. 

DIRECTIONS    FOR    STOPPING    DYNAMOS    AND    MOTORS. 

This  is  accomplished  by  following  substantially  the  same 
rules  as  those  given  for  starting  dynamos  and  motors  in 
Chapter  IV,  only  in  the  reverse  order.  But  there  are 
certain  peculiar  points  to  be  observed  in  each  case;  so,  in 
order  to  avoid  any  possible  mistake,  the  matter  of  stopping 
is  treated  in  this  separate  chapter.  After  any  machine  is 
stopped  it  should  be  thoroughly  cleaned  of  dirt,  copper 
dust  and  oil  and  put  in  perfect  order  for  the  next  run. 
Switches,  brushes,  etc.,  should  be  fixed  so  that  they  will 
not  accidentally  close  the  circuit. 

One  Constant  Potential  Dynanio  (Shunt, 
Series  or  Compound  Wound)  running  alone  on  a 
circuit  with  no  danger  of  receiving  current  from  any 
other  dynamo  or  battery,  should  be  slowed  down  and 
stopped  without  touching  the  switches,  brushes,  etc.,  in 
which  case  the  E.  M.  F.  and  current  decrease  gradually  to 
zero  as  the  speed  goes  down.  The  switches  may  then  be 
opened  and  the  brushes  lifted  without  any  spark.  In  the 
case  of  copper  brushes  this  should  be  done  just  before  the 
machine  stops  entirely,  in  order  to  avoid  any  injury  to 
them  if  the  machine  turns  back  a  little  as  sometimes  occurs. 
Never  switch  out  or  disconnect  a  dynamo  at  full  or  even 
partial  load  except  in  extreme  emergency,  and  the  brushes 
should  never  be  raised  while  the  fields  are  strongly  mag- 
netized as  the  discharge  of  the  magnetism  may  break  lamps 
or  pierce  the  insulation. 

Dynamos  in  Parallel. — To  stop  a  dynamo  run- 
ning in  parallel  with  one  or  more  others  or  with  a  storage 


Dynamos  and  Motors.  45 

battery  on  the  same  circuit  (usually  constant  potential) 
regulate  down  its  E.  M.  F.  until  it  is  only  slightly  greater 
than  that  of  the  circuit  (about  one  per  cent.)  and  its 
amperemeter  shows  that  it  is  producing  very  little  current; 
the  switch  connecting  it  to  the  circuit  should  then  be 
quickly  opened.  Under  no  circumstances,  however,  should 
a  dynamo  in  parallel  with  others  or  a  battery  be  stopped, 
slowed  down  or  have  its  field  magnetism  discharged  or 
weakened  (i.  e.,  more  than  enough  to  regulate  its  E.  M.  r. 
as  stated)  until  its  armature  is  completely  disconnected 
from  the  circuit,  as  it  might  be  burnt  out  or  driven  as  a 
motor  if  its  E.  M.  F.  fell  more  than  a  few  per  cent. 

Compound  Wound  Dynamos  in  Parallel 

may  be  stopped  by  exactly  reversing  the  method  for  start- 
ing (Fig.  13)  but  if  as  there  suggested  the  "equalizer" 
(E,  Fig.  13)  is  left  closed  all  the  time  the  machines  may 
then  be  stopped  like  simple  shunt  machines  in  parallel,  as 
just  described. 

Dynamos  on  the  Three-Wire  (Direct)  Sys- 
tem are  also  stopped  like  dynamos  on  any  constant  poten- 
tial circuit  as  explained  in  the  chapter  on  starting. 

Constant  Current  Dynamos  and  Motors  in 

series  may  be  cut  out  of,  or  into,  the  circuit  without  trouble 
and  may  be  slowed  down  or  stopped  without  disconnecting 
them  from  the  circuit  as  the  current  is  limited.  If  desired, 
the  field  coils  may  be  short-circuited  to  stop  the  action  of 
the  machine  while  in  circuit.  The  only  precaution,  and 
that  is  absolutely  imperative,  is  to  maintain  the  continuity 
of  the  circuit  and  never  attempt  to  open  it  at  any  point  as 
it  would  cause  a  dangerous  arc.  Hence  a  constant  current 
machine  must  be  cut  out  by  first  closing  the  main  circuit 
around  or  past  the  machine  and  then  entirely  disconnecting 
it  from  the  circuit,  that  is,  both  its  wires  or  terminals. 

One  Alternator  running  alone  on  a  circuit  may  be 
stopped  or  the  field  current  shut  off  without  trouble. 


46  Practical  Management  of 

Alternators  in  Parallel  may  be  disconnected 
from  the  circuit  without  the  difficulty  which  is  found  in 
throwing  them  on,  because  it  is  not  necessary  to  get  them 
in  phase. 

A  Constant  Potential  Motor  is  stopped  by  turn- 
ing the  starting  box  handle  back  to  the  position  it  had 
before  starting  (Fig.  IV)  or  if  there  is  a  switch  connecting 
motor  to  the  circuit  it  may  be  opened.  In  the  latter  case 
a  considerable  spark  will  occur,  but  if  it  is  a  c<  quick-break  " 
switch  it  may  be  better  able  to  stand  the  spark  than  the 
starting  box.  The  strictly  best  way  is  to  turn  the  starting 
or  regulating  box  arm  back  to  the  last  contact  point,  which 
puts  all  the  resistance  in  circuit,  and  then  open  the  quick- 
break  switch. 

Either  of  these  three  ways  is  perfectly  safe  and  the  one 
may  be  adopted  which  trial  shows  to  work  best  and  burn 
contact  points  the  least.  A  constant  potential  motor  like 
the  corresponding  dynamos  when  in  parallel,  should  never 
be  stopped  or  much  reduced  in  speed  or  have  its  field  dis- 
charged or  weakened  until  it  is  disconnected  from  the  cir- 
cuit, otherwise  its  counter  E.  M.  F.  is  not  enough  to  prevent 
an  excessive  current  from  rushing  through  its  armature. 

Thus  it  will  be  seen  that  the  constant  potential  machine 
is  exactly  the  opposite  of  the  constant  current.  The  former 
is  safest  when  the  circuit  is  open  and  it  is  very  bad  to  short- 
circuit  or  stop  it  with  the  current  on,  whereas  the  latter  is 
safest  when  the  circuit  is  closed,  and  the  machine  may  be 
stopped  or  short-circuited  while  in  circuit, 
stopped  or  short-circuited  while  in  circuit.  But  the  dyna- 
mo supplying  the  circuit  must  have  an  effective  regulator 
to  maintain  the  current  of  uniform  volume,  no  matter  how 
many  lamps  or  motors  are  cut  into  or  out  of  the  circuit. 


Dynamos  and  Motors.  47 


CHAPTER  VII. 

DIRECTIONS  FOR   TESTING   DYNAMOS   AND    MOTORS. 

The  matter  of  testing  dynamos  and  motors  is  of  special 
importance  since  it  is  only  by  a  thorough  test  that  either 
the  manufacturer  or  the  user  can  determine  whether  a  cer- 
tain machine  is  up  to  the  standard.  Nevertheless  it  is 
difficult,  if  not  impossible,  to  find  in  books  or  journals  any- 
thing like  a  complete  system  of  testing  methods  applicable 
to  dynamos  or  motors.  Each  electrical  manufacturer  or 
engineer  has  collected  by  experience  certain  methods,  but 
these  usually  apply  to  particular  forms  of  machine  or  test- 
ing apparatus  and  moreover  are  often  guarded  as  trade 
secrets. 

The  following  methods  cover  the  various  facts  about  a 
dynamo  or  motor  which  one  is  likely  to  want  to  test. 
Under  each  heading  exact  methods  are  given  which  should, 
of  course,  always  be  preferred;  but  wherever  possible  we 
have  also  given  simple,  rough  methods  for  emergencies  or 
other  cases  in  which  a  dynamo  or  motor  may  have  to  be 
tested  without  the  accurate  and  expensive  instruments  re- 
quired for  the  more  refined  methods. 

This  subject  differs  from  our  chapter  on  "  Locating  and 
Remedying  Troubles  in  Dynamos  or  Motors,"  in  the  fact 
that  the  other  relates  to  actual  faults  which  are  already 
apparent,  whereas  testing  applies  to  any  machine  whethei 
in  perfect  working  condition  or  containing  some  latent  fault 
which  a  test  brings  out  and  anticipates.  The  testing 
methods  here  given  can  also  be  used  as  supplementary  to 
the  methods  for  locating  troubles  in  cases  where  a  more 
complete  investigation  may  be  desirable.  In  testing  any 
machine  it  is  well  to  follow  as  nearly  as  possible  the  direc- 
tions given  by  its  maker  and  try  it  under  the  conditions 


48  Practical  Management  of 

for  which  it  is  intended,  in  regard  to  voltage,  current, 
speed,  etc.  Tests  of  dynamos  and  motors  may  cover  any 
or  all  of  the  following  points: 

1.  Adjustment  and  fit  of  parts. 

2.  Mechanical  Strength  of  parts  against  breaking 
or  displacement. 

3.  Friction  of  bearings  and  brushes. 

4.  Balance  of  armature  and  pulley. 

5.  Noise. 

6.  Electrical  Resistance  of  conductors  and  insu- 
lation. 

7.  Voltage,  E.  M.  F.,  "  drop  "  or  fall  of  potential,  etc. 

8.  Current  in  field,  armature  free  and  loaded. 

9.  Speed  of  armature,  free  and  loaded. 

10.  Torque  or  full)  standing  or  running. 

11.  Power 9  electrical  and  mechanical. 

12.  Efficiency,  electrical  and  commercial. 

13.  Seating  of  armature,  field  magnet,  bearings,  etc. 

14.  Sparking  at  commutator. 

15.  Magnetism,  total  flux,  intensity,  leakage    and 
distribution. 

16.  Line  or  Circuit  testing  for  resistance,  insula- 
tion, faults,  etc. 

1.  Adjustment  and  the  other  points  which  depend 
merely  upon  mechanical  construction  are  hardly  capable  of 
being  investigated  by  a  regular  quantitative  test,  but  they 
can  and  should  be  determined  by  thorough  inspection.  In 
fact  a  very  careful  examination  of  all  parts  of  a  machine 
should  always  precede  any  test  of  it.  This  should  be  done 
for  two  reasons,  first,  to  get  the  machine  into  proper  con- 


Dynamos  and  Motors.  49 

dition  for  a  fair  test,  and  second,  to  determine  whether  the 
materials  and  workmanship  are  of  first-class  quality  and 
satisfactory  in  every  respect.  A  loose  screw  or  connection 
might  interfere  with  a  good  test,  and  a  poorly  fitted  bearing, 
brush  holder,  etc.,  might  show  that  the  machine  was  badly 
made. 

If  it  is  necessary  to  take  the  machine  apart  for  cleaning 
or  inspection  the  greatest  care  should  be  exercised  in  mark- 
ing, numbering  and  placing  the  parts  in  order  to  be  sure 
to  get  them  together  in  exactly  the  same  position  as  before. 
In  taking  apart  or  putting  together  a  machine,  only  the 
minimum  force  should  be  used.  Much  force  usually  means 
that  something  wrong  is  being  done  or  in  a- wrong  way.  A 
wooden  mallet  is  preferable  to  an  iron  hammer,  since  it  does 
not  mar  or  strain  the  parts  so  much.  Usually  screws,  nuts 
and  other  parts  should  be  set  up  fairly  tight  but  not  tight 
enough  to  run  any  risk  of  breaking  or  straining  anything. 
Shaking  or  feeling  each  screw  or  other  part  will  'almost 
always  show  that  some  one  or  more  of  them  are  too  loose  or 
too  tight,  or  otherwise  out  of  adjustment. 

2.  Mechanical  Strength  of  a  dynamo  or  motor  is 
best  specified  by  stating  that  it  should  be  above  question. 
The  base,  bearings,  shaft,  armature,  field  magnets  and  other 
main  parts  of  the  machine  should  not  spring  even  one  one- 
hundredth  of  an  inch  with  any  reasonable  force  that  may 
be  applied  to  them.  There  has  long  existed  a  craze  for 
very  light  dynamos  and  motors,  as  a  result  of  which,  strength, 
rigidity,  durability  and  satisfactory  qualities  in  general 
have  been  sacrificed  to  reduce  weight.  There  is  certainly  no 
sense  in  this.  For  stationary  machines  and  even  for  ship 
dynamos  or  railway  motors  good  solid  frames,  bearings,  etc., 
are  much  better  than  light  ones. 

The  magnetic  attraction  between  the  field  and  armature 
is  often  very  great,  and  may  amount  to  hundreds,  or  even 
thousands,  of  pounds.  This  tends  to  draw  the  pole-pieces 
against  the  armature,  or  spring  the  armature  shaft  if  the 
armature  is  even  slightly  nearer  one  pole-piece  than  the 


50  Practical  Management  of 

other.  It  is  well  to  magnetize  the  field  by  putting  the 
proper  current  through  its  coils  and  see  if  it  produces  any 
reduction  of  the  clearance  or  other  displacement  that  is 
appreciable  to  the  eye  or  even  to  any  ordinary  measurement. 
The  effect  of  the  maximum  pull  of  the  belt  or  any  other 
legitimate  stress  may  be  tested  in  the  same  way. 

In  addition  to  this  all  the  parts  of  the  machine  should  be 
scrutinized  to  see  if  they  are  of  adequate  size  and  proper 
proportion. 

3.  Friction. — The  friction  of  the  bearings  and  brushes 
can  be  tested  roughly  by  merely  revolving  the  armature  by 
hand  and  noting  if  it  requires  more  than  the  normal  amount 
of  force.  Excessive  friction  is  quite  easily  distinguished 
even  by  inexperienced  persons.  Another  method  is  to  cause 
the  armature  to  revolve  by  hand  or  otherwise  and  see  if  it 
continues  to  revolve  by  itself  freely  for  some  time.  A  well- 
made  machine  in  good  condition  will  continue  to  run  for 
one  or  more  minutes  after  the  turning  force  is  removed. 

A  method  for  actually  measuring  the  friction  consists  in 
attaching  a  lever  (a  bar  of  wood,  for  example)  to  the  shaft 
or  pulley  at  right  angles  to  the  former.  The  force  re- 
quired to  overcome  the  friction  and  turn  the  armature 
without  current  is  then  determined  by  known  weights  or, 
more  conveniently,  by  an  ordinary  spring  balance.  The 
friction  of  the  bearings  alone,  that  is,  the  pull  required  to 
turn  the  armature  when  the  brushes  are  lifted  off  the 
commutator  and  there  is  no  current  or  magnetism  in  the 
field,  should  not  exceed  1  per  cent,  of  the  total  torque  or 
turning  force  of  the  machine  at  full  load.  When  the 
brushes  are  in  contact  with  the  commutator  with  the  usual 
pressure,  the  friction  should  then  not  exceed  2  per  cent., 
that  is,  the  brushes  themselves  should  not  consume  more 
than  1  per  cent,  of  the  total  turning  force.  When  the  field 
magnetism  is  at  full  strength,  and  the  brushes  are  on  the 
commutator,  the  maximum  friction  or  pull  required  to 
turn  the  armature  should,  then,  not  exceed  4  per  cent. 
of  the  total  torque. 


Dynamos  and  Motors.  51 

This  torque  or  pull  in  pounds  in  the  case  of  any  machine 
may  be  calculated  by  the  formula  : 

H.  P.  X  33,000 
Torque  =  ^g  y  J{  y  ^ 

in  which  H.  P.  is  the  horse  power  of  the  machine  at  full 
load,  R  is  the  radius  or  length  in  feet  of  the  lever  used  in 
the  test,  and  S  is  the  speed  of  the  machine  in  revolutions 
per  minute  at  full  load. 

Another  method  of  measuring  the  friction  of  a  machine 
is  to  run  it  by  another  machine  used  as  a  motor  and  de- 
termine the  volts  and  amperes  required,  first,  with  brushes 
lifted  off  and  no  field  magnetism  ;  second,  with  brushes  on 
commutator  but  no  magnetism ;  and  third,  with  full 
strength  of  field  magnetism  giving  maximum  friction.  The 
torque  or  force  exerted  by  the  driving  machine  is  after- 
wards measured  by  a  Prony  brake  in  the  manner  described 
hereafter  for  testing  torque  ;  care  being  taken  to  make  the 
Prony  brake  measurements  at  exactly  the  same  volts  and 
amperes  as  were  required  in  the  friction  tests.  In  this 
way  the  torques  which  were  exerted  by  the  driving  machine 
to  overcome  friction  in  each  of  the  three  first  tests  are 
determined,  and  these  torques  compared  with  the  total 
torque  of  the  machine  being  tested,  as  calculated  by  the 
formula  just  given,  should  give  percentages  not  exceeding 
those  stated  above  for  the  maximum  values  of  friction. 

Tests  for  friction  alone  should  be  made  at  a  low  speed 
because  at  high  speeds  the  effect  of  Foucault  currents  and 
hysteresis  enter  and  materially  increase  the  apparent 
friction. 

4.  Balance. — The  perfection  of  balance  of  the  arma- 
ture or  pulley  can  be  roughly  tested  by  simply  running  the 
machine  at  its  normal  speed  and  noting  if  these  parts  are 
sufficiently  well  balanced  not  to  cause  any  objectionable 
vibration.  Of  course,  practically  every  machine  produces 
perceptible  vibration  when  running,  but  this  should  not  be 


52  Practical  Management  of 

more  than  a  slight  trembling.  The  balance  of  a  machine 
can  be  definitely  tested  and  the  extent  of  the  vibration 
measured  by  suspending  the  machine  or  mounting  it  on 
wheels  and  running  it  at  full  speed.  In  this  case  it  is 
better  to  run  the  machine  as  a  motor,  even  though  it  be 
actually  a  dynamo,  in  order  to  make  it  produce  its  own 
motion,  so  to  speak,  and  avoid  the  necessity  of  running  it 
by  a  belt  which  would  cause  vibration  and  interfere  with 
the  test.  If,  however,  the  use  of  a  belt  is  unavoidable,  it 
should  be  arranged  to  run  vertically  upward  or  downward 
so  as  not  to  produce  any  horizontal  motion  in  addition  to 
the  vibration  of  the  machine  itself.  Fig.  21  shows  a 
machine  hung  up  to  be  tested  for  balance  and  run  either  as 
a  motor  or  by  the  vertical  belt  indicated  as  a  dotted  line. 
Any  lack  of  balance  will  cause  the  machine  to  vibrate  or 
swing  horizontally,  and  this  motion  can  be  measured  on  a 
fixed  scale. 

5.  Noise. — This  cannot  be  well  tested  quantitatively, 
although  it  is  very  desirable  that  a  machine  should  make 
as  little  noise  as  possible.     Noise  is  produced  by  the  vari- 
ous causes  given  in  the  chapters  on  Locating  Faults.     The 
machine  should  be  run  at  full  speed  and  any  noise  and  its 
cause  carefully  noted. 

6.  Electrical  Resistance. — There  are  two  principal 
classes  of  resistance  tests  that  have  to  be  made  in  connec- 
tion with  dynamos  and   motors.     First,  the   resistance  of 
the  wires  or  conductors  themselves,  which  might  be  called 
the  metallic  resistance;  and  second,  the  resistance  of  the 
insulation  of  the  wires,  which  is  called  the  insulation  re- 
sistance.    The  former  should  usually  be  as  low  as  possible, 
the   latter    should    always   be   as   high    as    possible,   be- 
cause a  low  insulation  resistance  not  only  allows  current 
to  leak,  but  also  causes  "  burn-outs  "  and  other  accidents. 
Metallic  resistance,  such,  for  example,  as  the  resistance  of 
the  armature  or  field  coils,  is  commonly  tested  either  by  the 
Wheatstone   bridge   or  the    "drop"    (fall    of    potential) 
method. 


Dynamos  and  Motors. 


53 


The  Wheatstone  bridge,  Fig.  23,  is  simply  a  number  of 
branch  circuits  connected  as  indicated  in  Fig.  22.  A,  B  and 
c  are  resistances  the  values  of  which  are  known.  D  is  the 


resistance  which  is  being  measured.  G  is  a  galvanometer 
and  E  is  a  battery  of  one  or  two  cells  controlled  by  a  key 
K,  all  being  connected  exactly  as  shown.  The  resistance  c 
is  varied  until  the  galvanometer  shows  no  deflection  when 


54  Practical  Management  of 

the  key  K  is  closed.  The  value  of  the  resistance  D  is  then 
found  by  multiplying  together  resistances  c  and  B  and  divid- 

n  s/  n 

ing  by  A;  that  is,  D  =  _  - —  A  very  convenient  form  of  this 

apparatus  is  what  is  known  as  the  portable  bridge.  This 
consists  of  a  box  containing  the  three  sets  of  known  resist- 
ances A,  Band  c  con  trolled  by  plugs,  also  the  galvanometer  G 
and  key  K,  all  connected  in  the  proper  way.  In  some  cases 
the  perfection  of  convenience  is  reached  by  including  the 
battery  E  in  the  box  also,  but  ordinarily  this  is  not  done 
and  it  is  necessary  to  connect  one  or  two  cells  of  battery 
to  a  pair  of  binding  posts  placed  on  the  box  for  that  purpose. 
Resistances  from  -^  ohm  to  100,000  ohms  can  be  con- 
veniently  and  accurately  measured  by  the  Wheatstone  bridge. 
Below  -fa  ohm  the  resistances  of  the  contacts  in  the  binding 
posts  and  plugs  are  apt  to  cause  errors.  In  fact,  in  measuring 
any  resistance  care  should  be  taken  to  make  the  connections 
clean  and  tight.  The  ordinary  bridge  will  not  measure  above 
100,000  ohms  because  if  the  resistance  in  the  arm  B  is  100 
ohms,  1  ohm  in  A,  and  1,000  ohms  in  c,  then  D  is  100,000. 
Sometimes  the  arms  A  and  B  are  provided  with  1,000-ohm 
coils  in  addition  to  the  usual  1,  10  and  100  ohm  coils,  or 
sometimes  the  arm  c  contains  more  than  1,000  ohms  in  all; 
in  either  case  the  range  will  be  correspondingly  increased. 
The  bridge  may  be  used  for  testing  the  resistance  of  almost 
any  field  coils  that  are  found  in  practice.  Shunt  fields  for 
110-volt  machines  usually  vary  from  about  100  or  200 
ohms  in  a  1  h.  p.  machine  to  about  10  or  20  ohms  in  a  100 
h.  p.  machine.  If  the  voltage  is  higher  or  lower  than 
110  these  resistances  vary  in  direct  proportion.  Series1 
fields  for  arc  circuit  dynamos  ©r  motors  vary  from  about 
1  to  20  ohms. 

The  bridge  may  also  be  used  for  testing  the  armature 
resistance  of  most  machines.  But  110-volt  shunt  machines 
above  10  h.  p.  usually  have  resistances  below  -fa  ohm,  which 
is  below  the  range  of  the  bridge,  as  already  stated.  Higher 
voltage  dynamos  and  motors  have  proportionally  higher 


Dynamos  and  Motors.  55 

resistance  armatures.  Arc  machines  have  armatures  of 
about  1  to  20  ohms  resistance  and  are  therefore  easily 
tested  by  the  bridge. 

The  "  drop  "  or  fall  of  potential  method  is  well  adapted  to 
testing  the  armature  resistance  of  large  incandescent  dyna- 
mos or  the  resistance  of  contact  between  commutator  and 
brushes  or  other  resistances  which  are  usually  only  a  few 


FIG.  23.— PORTABLE  WHEATSTONE  BRIDGE. 

hundredths  or  even  thousandths  of  an  ohm.  This  consists 
in  passing  a  current  through  the  armature  and  a  known 
resistance  of,  say,  y^  ohm  connected  in  series  with  each 
other,  as  represented  in  Fig.  24.  The  "  drop  "  or  fall  of 
potential  in  the  armature  and  in  the  known  resistance  are 
then  compared  by  connecting  a  galvanometer  first  to  the 
terminals  marked  1  and  2  and  then  to  3  and  4.  The  de- 
flections of  the  needle  in  the  two  cases  are  proportional  to 


56 


Practical  Management  of 


the  resistances.  The  current  needed  depends  upon  the 
sensitiveness  of  the  galvanometer,  but  should  not  require 
more  than  a  few  cells  of  battery.  If  a  galvanometer  is  not 
at  hand,  the  drop  method  can  be  used  with  a  strong  current 
and  a  voltmeter,  the  connections  being  the  same  as  in 
Fig.  23.  The  current  required  in  this  case  depends  upon 
the  resistance  to  be  measured,  but  it  must  of  course  be  suf- 
ficient to  produce  a  readable  deflection  on  the  voltmeter. 
Usually  10  to  100  amperes  and  a  voltmeter  reading  to  a 
single  volt  or  fractions  of  one  volt  are  needed  for  low 
resistances. 

It  is  wise  to  start  with  a  small  current   and  increase   it 
until  a  reasonably  readable  deflection  is  obtained  on  the 


OWN   RESISTANCE 


FIG.  24. 


voltmeter.  The  current  may  be  obtained  by  using  a  cell 
of  storage  battery,  or  a  few  cells  of  some  strong  primary 
battery  such  as  a  plunge  battery,  Bunsen  or  bichoromate 
battery.  The  current  may  also  be  taken  from  another 
dynamo  or  from  a  circuit,  but  a  bank  of  lamps  or  a  liquid 
resistance  should  then  be  used  to  control  the  current,  as  the 
armature  alone,  of  course,  has  very  little  resistance.  A  con- 
venient form  of  liquid  resistance  for  this  purpose  is  described 
hereafter  in  the  directions  for  testing  current  (No.  8.) 

The  insulation  resistance  of  a  dynamo  or  motor,  that  is, 
the  resistance  between  its  wires  and  its  frame  should  be  at 
least  one  megohm  per  hundred  volts  E.  M.  F.,  and  it  is,  of 


Dynamos  and  Motors. 


57 


course,  better  if  it  is  much  higher.  It  is  therefore  beyond 
the  range  of  ordinary  Wheatstone  bridge  tests,  but  there 
are  two  good  methods  which  are  applicable — the  "direct 
deflection "  method  and  the  voltmeter  method.  The 
direct  deflection  method  is  carried  out  by  connecting  a 
sensitive  galvanometer  such  as  a  Thomson  high  resistance 
reflecting  galvanometer  (tripod  or  square  pattern)  in  series 
with  a  known  high  resistance,  usually  a  100,000  ohm 
rheostat,  a  battery  and  a  key  as  shown  in  Fig.  25.  The 
galvanometer  should  be  shunted  with  the  ^¥  coil  of  the 
shunt  so  that  only  T^oT  °f  tne  current  passes  through  the 
galvanometer,  the  machine  being  entirely  disconnected. 
The  key  is  closed  and  the  steady  deflection  noted.  It  is 
well  to  use  only  one  cell  of  battery  at  first  and  then  increase 


GALVANOMETER 


Fia.  26. 

the  number  if  necessary  until  a  considerable  deflection  is 
obtained.  One  of  the  wires  is  then  connected  to  the  binding 
post  or  commutator  of  the  dynamo  or  motor  and  the 
other  to  the  frame  or  shaft  of  the  machine  as  indicated  by 
dotted  lines.  The  key  is  closed  and  the  deflection  noted. 
Probably  there  will  be  little  or  no  deflection  on  account  of 
the  high  insulation  resistance,  and  the  shunt  is  changed  to 
•g^,  $  or  left  out  entirely  if  little  deflection  is  obtained.  In 
changing  the  shunt,  the  key  should  always  be  open,  other- 
wise the  full  current  is  thrown  on  the  galvanometer.  The 
insulation  is  then  calculated  by  the  formula:  Insulation 

T)  v  7?  v  K 

resistance  =        A    ^  A    ,  in  which  D  is  the  first  deflection 
d 

without  the  machine  connected  and  d  the  deflection  with 


58 


Practical  Management  of 


the  insulation  in  the  circuit,  R  the  known  high  resistance 
and  S  the  ratio  of  the  shunt.  That  is,  if  the  shunt  is  -^  9 
in  the  first  test  and  %  in  the  second,  then  /Sis  100,  and 
if  the  shunt  is  out  entirely  in  the  second  test  S  is  1,000.  It 
is  safer  to  leave  the  high  resistance  in  circuit  in  the  second 
test  to  protect  the  galvanometer  in  case  the  insulation 
resistance  is  low.  Therefore  this  resistance  must  be  sub- 
tracted from  the  result  to  obtain  the  insulation  itself.  By 
the  above  method  it  is  possible  to  measure  100  megohms, 
or  even  more.  The  wires  and  connections  should  be  care- 
fully arranged  to  avoid  any  possibility  of  contact  or  leakage 
which  would  spoil  the  test. 

The  voltmeter  test  for  insulation  resistance  requires  a 
sensitive   high  resistance  voltmeter  such  as  the  Weston. 


Take,  for  example,  the  150- volt  instrument  which  usually 
has  about  15,000  ohms  resistance;  apply  it  to  some  circuit  or 
battery  and  measure  the  voltage.  This  should  be  as  high 
as  possible;  say,  100  volts.  The  insulation  resistance  of  the 
machine  is  then  connected  into  the  circuit  as  indicated  in 
Fig.  26.  The  deflection  of  the  voltmeter  is  then  reduced 
in  proportion  to  the  value  of  the  insulation  resistance. 
The  insulation  is  then  found  by  the  equation  :  Insulation 

resistance  =  — ^ R,  in  which  D  is  the  first,  and 

d  the  second  deflection  and  R  the  resistance  of  the  volt- 


Dynamos  and  Motors.  59 

meter.  If  the  circuit  is  100  volts  then  D  is  100  ;  and  if  d, 
the  deflection  through  the  insulation  resistance  of  the 
machine,  is  1  division,  then  the  insulation  is:  (100  X  15,000) 
— 15,000  =  1,485,000  ohms.  This  method  does  not  test 
very  high  resistances,  but  if  little  or  no  deflection  is  obtained 
through  the  insulation  resistance  it  shows  that  it  is  at  least 
several  megohms,  which  is  high  enough  for  practical 
purposes. 

The  ordinary  magneto  bell  may  be  used  to  test  insulation 
by  simply  connecting  one  terminal  to  the  binding  post  of 
the  machine  and  the  other  to  the  frame  or  shaft. 

A  magneto  bell  is  rated  to  ring  through  a  certain  resist- 
ance, usually  from  10,000  to  30,000  ohms,  and  if  it  does  not 
ring  it  shows  that  the  insulation  is  more  than  that  amount. 
This  limit  is  altogether  too  low  for  proper  insulation  in 
any  case,  and  therefore  this  test  is  rough  and  really  only 
shows  whether  the  insulation  is  very  poor  or  the  machine 
actually  grounded. 

7.  Voltage. — There  is  no  convenient  way  of  testing 
voltage  except  by  means  of  a  voltmeter.  Unfortunately 
a  really  satisfactory  voltmeter  is  rather  an  expensive  in- 
strument. A  good  voltmeter  should  be  very  accurately 
calibrated  because  an  error  of  one  per  cent,  in  the  voltage 
of  an  incandescent  circuit  is  objectionable,  whereas  the  same 
error  would  be  insignificant  in  almost  any  other  practical 
measurement.  A  voltmeter  should  have  as  high  a  resistance 
as  possible — at  least  several  hundreds  or  thousands  of  ohms — 
in  order  not  to  take  too  much  current  which  might  lower 
its  reading  on  a  high  resistance  circuit.  It  should  not  be 
affected  by  the  magnetism  of  a  dynamo  or  motor  at  any 
distance  over  four  or  five  feet.  The  voltage  of  any  machine 
or  circuit  is  tested  by  merely  connecting  the  two  binding 
posts  or  terminals  of  the  voltmeter  to  the  two  terminals 
or  conductors  of  the  machine  or  circuit.  In  the  case  of  a 
dynamo  or  motor  the  voltmeter  is  usually  applied  to  the 
two  main  binding  posts  or  brushes  of  the  machine  to  get 
the  external  voltage  of  the  machine.  This  external  voltage 


60  Practical  Management  of 

is  what  a  dynamo  supplies  to  the  circuit  and  it  is  what  a 
motor  receives  from  the  circuit.  This  is  called  the  pole 
difference  of  potential  or  terminal  voltage  and  is  the  actual 
figure  upon  which  calculations  of  the  efficiency,  capacity, 
etc.,  of  any  machine  are  based. 

A  dynamo  for  constant  potential  circuits  should,  of  course, 
give  as  nearly  as  possible  a  constant  voltage.  A  plain  shunt 
machine  usually  falls  from  3  to  10  per  cent,  in  voltage  when 
its  current  is  varied  from  nothing  to  full  load.  This  is  due 
to  the  loss  of  voltage  in  the  resistance  of  the  armature, 
which  in  turn  weakens  the  field  current  and  magnetism; 
armature  reaction  and  reduction  in  speed  usually  occur  also 
and  still  further  lower  the  external  voltage,  but  of  course 
this  variation  is  very  undesirable.  A  com  pound -wound 
dynamo  should  not  fall  appreciably  from  no  load  to  full 
load;  in  fact,  if  it  is  "over-compounded,"  it  should  rise  two 
or  three  per  cent,  in  voltage  to  make  up  for  loss  on  the 
wiring.  The  voltage  of  a  constant  current  dynamo  or  motor 
is  not  important.  The  current  should  be  carefully  measured 
by  an  amperemeter,  but  little  or  no  attention  is  paid  to  the 
voltage  in  practical  working;  in  fact,  it  changes  constantly 
with  variations  in  the  load.  It  is  of  course  necessary, 
however,  to  measure  it  for  a  test  of  efficiency  or  other 
exact  tests. 

A  very  simple  and  fairly  accurate  method  of  measuring 
voltage  is  by  means  of  ordinary  incandescent  lamps.  A 
little  practice  enables  one  to  tell  whether  a  lamp  has  its 
proper  voltage  and  brightness.  In  this  way  it  is  easy  to 
tell  if  the  voltage  is  even  one  or  two  per  cent,  above  or 
below  the  normal  point.  Voltages  less  than  the  ordinary 
can  be  tested  by  using  low  voltage  lamps  or  by  estimating 
the  brightness  of  high  voltage  lamps.  For  example,  a 
lamp  begins  to  show  a  very  dull  red  at  one-third  and  a  bright 
red  at  one-half  its  full  voltage.  Voltages  higher  than  that 
of  one  lamp  can  be  tested  in  this  way  by  using  lamps  in 
series.  In  fact,  even  1, 000  or  more  volts  can  be  measured 
by  using  10  or  more  lamps  in  series. 


Dynamos  and  Motors.  61 

8.  Current. — This  is,  of  course,  measured  by  means 
of  an  amperemeter,  and  this  instrument  is  usually  cheaper 
than  a  voltmeter  because  it  only  contains  a  compara- 
tively small  amount  of  wire,  and  does  not  ordinarily 
require  to  be  accurate  within  one  or  two  per  cent.  In  test- 
ing the  current  of  a  dynamo  or  motor  all  that  is  necessary 
is  to  connect  an  amperemeter  of  the  proper  range  in  series 
with  the  machine  to  be  tested  so  that  the  whole  current  to 
be  measured  passes  through  the  instrument.  To  test  the 
current  in  the  armature  or  field  alone,  the  amperemeter  is 
connected  in  series  with  the  particular  part.  In  the  case  of 
a  shunt-wound  dynamo  it  is  well  to  entirely  open  the 
external  circuit  in  testing  the  current,used  in  the  field  coils 
in  order  to  avoid  mistake,  for  the  same  reason  the  brushes 
of  a  shunt  motor  should  be  raised  while  testing  the  current 
taken  by  the  field.  In  a  constant  current  (series  wound) 
dynamo  or  motor  the  same  current  flows  through  all  parts 
of  the  machine  and  the  rest  of  the  circuit,  consequently  the 
measurement  of  current  is  very  simple. 

In  testing  the  current  produced  by  a  dynamo  it  is  often 
quite  a  problem  to  consume  it.  A  bank  of  lamps,  for  ex- 
ample, to  use  the  whole  current  generated  by  a  dynamo  of 
110  volts  and  200  amperes  would  be  very  expensive.  A 
sufficient  number  of  resistance  boxes  for  the  purpose  would 
also  be  very  costly.  The  simplest  and  cheapest  means  to 
consume  a  large  current  is  to  place  two  plates  of  metal  or 
carbon  in  a  common  tub  or  trough  filled  with  a  very 
dilute  solution  of  sulphate  of  soda  or  sulphuric  acid. 
The  main  conductors  are  connected  to  the  two  plates,  respec- 
tively, and  the  current  passed  through  the  solution.  The 
resistance  and  current  are  regulated  by  varying  the  dis- 
tance between  the  plates  and  the  depth  they  are  immersed 
in  the  liquid.  The  energy  may  be  sufficient  to  boil  the 
liquid  but  this  does  no  harm.  As  high  as  three  amperes 
per  sq.  inch  of  exposed  surface  may  be  allowed.  Strengthen 
solution  or  move  plates  together  for  low  voltages. 

Q.  Speed. — This  is  usually  tested  by  the  well-known 
speed  meter  or  speed  counter  which  consists  merely  of  a 
little  spindle  which  turns  a  wheel  one  tooth  each  time  it 


6£  Practical  Management  of 

revolves.  The  point  of  the  spindle  is  held  against  the 
centre  of  the  shaft  of  the  dynamo  or  motor  for  a  certain  time, 
say,  one  minute  or  one-half  minute,  and  the  number  of 
revolutions  is  read  off  from  the  position  of  the  wheel. 

Another  instrument  for  measuring  number  of  revolutions 
per  minute  is  the  tachometer.  The  stationary  form  of  this 
instrument  is  shown  in  Fig.  27.  This  requires  to  be  belted 
by  a  string,  tape  or  light  leather  belt  to  the  machine  the 
speed  of  which  is  to  be  tested.  If  the  sizes  of  the  pulleys 
are  not  the  same,  their  speeds  are  inversely  proportional  to 
their  diameters.  The  portable  form  of  this  instrument  is 
applied  directly  to  the  end  of  the  shaft  of  the  machine 


FIG.  27. 

like  the  speed  meter.  These  instruments  possess  the  great 
advantage  over  the'  speed  meter  that  they  instantly  point 
on  the  dial  to  the  proper  speed  and  they  do  not  require  to 
be  timed  for  a  certain  period. 

A  simple  way  to  test  revolutions  per  minute  is  to  make 
one  large  black  or  white  mark  on  the  belt  of  a  machine  and 
note  how  many  times  the  mark  passes  per  minute;  the 
length  of  the  belt  divided  by  the  circumference  of  the 
pulley  gives  the  number  of  revolutions  of  the  pulley  for 
each  time  the  mark  passes.  If  the  machine  has  no  belt, 
it  can  be  supplied  with  one  temporarily  for  the  purpose  of 
the  test,  a  piece  of  tape  with  a  knot  or  an  ink  mark  being 


Dynamos  and  Motors. 


63 


sufficient.  Care  should  be  taken  in  all  these  tests  of  speed 
with  belts,  not  to  allow  any  slip;  for  example,  in  the  case  of 
the  tape  belt  just  referred  to,  it  should  pass  around  the 
pulley  of  the  machine  and  some  light  wheel  of  wood  or 
metal  which  turns  so  easily  as  not  to  cause  any  slip  of  the 
belt  on  the  pulley  of  the  machine. 

10.  Torque  or  full  is  tested  in  the  case  of  a  motor 
by  the  use  of  a  Prony  brake.     This  consists  of  a  lever  L  L 


FIG. 


of  wood  clamped  on  to  the  pulley  or  shaft  of  the  machine 
to  be  tested,  as  indicated  in  Fig.  28.  The  pressure  of  the 
screws  s  s  is  then  adjusted  by  the  wing  nuts  until  the  fric- 
tion of  the  clamp  on  the  pulley  is  sufficient  to  cause  the 
motor  to  take  a  given  current  and  run  at  a  given  speed. 
Usually  the  maximum  torque  or  pull  is  the  most  important 
to  test  and  this  is  obtained  in  the  case  of  a  constant  poten- 
tial motor  by  tightening  the  screws  s  s  until  the  motor 
draws  its  full  current  as  indicated  by  an  amperemeter. 
What  the  full  current  should  be,  is  usually  marked  on  the 


64  Practical  Management  of 

name  plate;  if  not,  it  maybe  assumed  to  be  about  8  amperes 
per  h.  p.  for  110- volt  motors,  4  amperes  per  h.  p.  for  220- 
volt  and  If  ampere  per  h.  p.  for  500-volt  motors.  The 
torque  or  pull  is  then  measured  by  known  weights,  or  more 
conveniently  by  a  spring  balance  p.  If  desired,  the  test 
may  also  be  made  at  three-quarters,  one-half  or  any  other 
fraction  of  the  full  current. 

The  torque  or  pull  of  a  constant  current  mrtor  is  found 
by  adjusting  the  screws  s  s  until  the  armature  runs  at  its 
normal  speed. 

The  torque  or  pull  of  a  dynamo,  that  is,  the  force  required 
to  drive  it,  is  tested  by  a  transmission  dynamometer.  There 
are  several  forms  of  this  apparatus  but  none  of  them  are 
very  satisfactory.  In  the  cradle  dynamometer  the  dynamo 
is  placed  on  a  platform  which  is  hung  on  a  pivot  or  ful- 
crum. The  axis  of  the  shaft  of  the  dynamo  is  adjusted  so 
that  it  exactly  coincides  with  the  axis  of  the  pivot  or  ful- 
crum. When  the  dynamo  is  run  by  a  vertical  belt,  the 
pull  or  torque  tends  to  cause  the  dynamo  to  turn  about 
its  axis  of  suspension,  and  the  force  of  this  torque  is 
measured  by  the  amount  of  weights  required  to  keep  the  dy- 
namo and  platform  horizontal.  In  a  modified  form  of  the 
cradle  dynamometer  the  dynamo  is  placed  in  a  water-tight 
box  which  floats  in  another  box  filled  with  water,  instead 
of  being  hung  on  a  pivot.  It  is  usually  much  easier  to 
test  the  torque  of  a  dynamo  by  running  it  as  a  motor  and 
testing  it  by  the  Prony  brake  method  described  above.  The 
torque  of  a  dynamo  is  practically  equal  to  that  of  a  motor 
under  identical  conditions. 

11.  Power. — The  electrical  power  of  a  dynamo  or 
motor  is  found  by  testing  the  voltage  and  current  at  the 
terminals  of  the  machine,  as  described  in  sections  7  and  8  of 
this  chapter,  and  multiplying  the  two  together,  which  gives 
the  electrical  power  of  the  machine  in  watts.  These  watts 
divided  by  746  are  then  converted  into  horse  power,  thus  : 

TT  volts  X   amperes 

Horse  power  =  -       -2- —        — 


Dynamos  and  Motors.  65 

The  mechanical  power  of  a  dynamo  or  motor,  that  is,  the 
power  required  for  or  developed  by  it  is  found  by  multiply- 
ing its  torque  or  pull,  determined  as  described  in  the  previous 
paragraph,  by  its  speed,  determined  as  described  in  section 
9  of  the  present  chapter,  and  by  the  circumference  of  the 
circle  on  which  the  torque  is  measured,  and  dividing  by 
33,000,  that  ii 


Horse  power  =  P  X  S  X   6>28  X  ^in  which  Pis  the  torque 
33.000 

in  pounds,  S  the  speed  in  revolutions  per  minute  and  R  the 
radius  at  which  P  is  measured. 

12.  Efficiency* — This  is  determined  in  the  case  of  a 
dynamo  by  comparing  the  mechanical  power  required  to 
drive  it  by  the  electrical  power  generated  by  it,  that  is — 

Efficiency  of  dynamo  =   Electricalpowei^ 
Mechanical  power 

The  efficiency  of  a  motor  is  the  mechanical  power  developed 
by  it  divided  by  the  electrical  power  supplied  to  it,  that  is — 
Efficiency  of  motor  =  Mechanical  power 
Electrical  power 

These  are  the  actual  or  commercial  efficiencies  of  these 
machines  and  should  be  about  90  per  cent,  in  machines  of 
10  h.  p.  and  over. 

The  so-called  "  electrical  efficiency "  is  misleading  and 
of  little  practical  importance  and  should  not  be  considered 
in  commercial  work.  The  mechanical  and  electrical  power 
in  the  above  equations  are  determined  as  described  in 
the  last  section. 

13.  Heating.— This  is  measured  by  applying  a  thermo- 
meter to  the  various  parts  of  the  machine,  after  it  has  run 
at  full  load  for  one  or  two  hours,  in  fact  a  large  machine 
does  not  reach  its  maximum  temperature  until  it  has  run 
for  three  or  four  hours. 

The  bulb  of  the  thermometer  is  applied  directly  to  the 
surface  of  the  field  coil  or  other  part.  To  test  the  armature 


66  Practical  Management  of 

it  must,  of  course,  be  stopped.  The  thermometer  bulb 
should  be  covered  over  with  a  bunch  of  waste  or  cloth  to 
keep  in  the  heat.  The  temperature  of  the  armature,  field 
coils,  bearings,  etc.,  should  not  rise  more  than  40°  C.  or 
72°  F.  above  that  of  the  surrounding  air.  A  very  simple  test 
of  heating  is  to  apply  the  hand  to  the  armature,  etc.,  and 
if  it  can  be  kept  on  without  great  discomfort,  the  temper- 
ature is  perfectly  safe.  (See  "  Heating "  in  chapters  on 
Locating  Faults.) 

14.  Sparking  at  the  commutator  cannot  be  actually 
measured,  but  it  is  a  very  important  matter  and  in  any  test 
it  should  be  carefully  observed  whether  the  sparking  is 
excessive  or  not,  and  if  so,  what  it  is  due  to.    (See  * '  Spark- 
ing" in  chapters  on  Locating  Faults.) 

15.  Magnetism. — Magnetic  measurements  are  dim- 
cult  to  make  with  the  ordinary  apparatus  used  in  practical 
work.     The  proper  method  of  testing  magnetism  is  with 
the  ballistic  galvanometer.     To  test  the  magnetic  leakage 
in  a  dynamo  or  motor,  for  example,  a  coil  of  wire  connected 
to  the  galvanometer  is  put  around  the  field  magnet  and  the 
current  in  the  field  is  stopped  the  deflection  of  the  galvano- 
meter needle  being  noted.  A  coil  of  the  same  number  of  turns 
is  then   put  around  the  armature  and  the  swing  of  the 
galvanometer  is  again  noted.     The  first  deflection  is  to  the 
second  as  the  number  of  lines  of  magnetic  force  in  the  field 
is  to  those  in  the  armature,  provided  the  angles  of  deflection 
are  only  a  few  degrees. 

An  ordinary  detector  galvanometer  can  be  used  for  this 
work  if  it  is  not  damped  by  wings  to  prevent  its  swinging 
freely.  A  low- voltage  Weston  voltmeter  or  the  calibration 
coil  of  a  high-reading  one,  can  also  be  used  very  con- 
veniently for  magnetic  measurements  in  place  of  the  galvano- 
meter as  described  by  A.  S.  Ives  in  the  Electrical  World, 
Jan.  2,  1892. 

16.  Line   or    Circuit  testing  for  resistance,  insu- 
lation, current,  voltage,  etc.,  is  performed  by  exactly  the 


Dynamos  and  Motors.  67 

same  methods  as  those  just  described  for  making  the  cor- 
responding tests  on  dynamos  and  motors.  For  example,  in 
testing  the  insulation  resistance  of  a  line  or  circuit,  one 
wire  is  connected  to  the  line  and  the  other  to  the  ground 
(a  gas  or  water  pipe  is  convenient  for  this  purpose)  instead 
of  connecting  one  wire  to  the  commutator  and  the  other  to 
the  frame  of  the  machine  as  described  for  testing  the  insu- 
lation resistance  of  a  dynamo,  otherwise  the  test  is  exactly 
the  same. 


THE 

LOCALIZATION  AND  REMEDY 

OF 

TROUBLES  IN  DYNAMOS  OR  MOTORS. 


INTRODUCTION. 

THE  promptness  and  ease  with  which  any  accident  or 
difficulty  with  electrical  machinery  may  be  dealt  with, 
whether  by  the  inspector  of  construction  or  by  the  opera- 
tor in  charge  of  running,  will  always  have  much  to  do  with 
the  success  of  the  plant  and  of  those  dependent  upon  it. 
It  is  therefore  likely  that  any  method  to  eliminate  or  re- 
duce these  troubles  would  be  very  welcome  to  those 
handling  dynamos  and  motors.  With  the  object  of  ob- 
taining such  a  method,  we  have  prepared  a  list  of 
troubles,  symptoms  and  remedies,  based  upon  quite  an,  ex- 
tensive experience  with  the  various  types  and  sizes  of  dyna- 
mos and  motors  in  common  use. 

It  is  evident  that  this  subject  is  somewhat  complicated 
and  difficult  to  handle  in  a  general  way,  since  so  much  de- 
pends upon  the  particular  conditions  in  any  given  case, 
every  one  of  which  must  be  included  in  the  table  in  such 
a  way  as  to  distinguish  it  from  all  others.  Nevertheless, 
it  is  quite  remarkable  how  much  can  be  covered  by  a  system- 
atic and  reasonably  simple  statement  of  the  matter,  and 
we  feel  confident  that  nearly  all  of  the  cases  of  trouble 
most  likely  to  occur  are  covered  by  the  table,  and  that  the 


2  Localization  and  Remedy 

detection   and  remedy   of  the  defect  will  result  from  a 
proper  application  of  the  rules  given. 

It  frequently  happens  that  a  trifling  oversight,  such  as 
allowing  a  wire  to  slip  out  of  a  binding-post,  will  cause  as 
much  annoyance  and  delay  in  the  use  of  electrical  machin- 
ery as  the  most  serious  accident.  Other  troubles,  equally 
simple  but  not  as  easily  detected,  are  of  frequent  occur- 
rence. In  such  cases  a  very  slight  knowledge  on  the  part 
of  a  man  having  the  machine  in  charge,  guided  by  a  cor- 
rect set  of  rules,  will  enable  him  to  overcome  the  difficulty 
immediately  and  save  much  time,  trouble  and  expense. 

It  must  not  be  supposed  that  this  method  for  treating 
dynamo  and  motor  troubles  is  given  because  these  machines 
are  particularly  liable  to  such  difficulties.  On  the  contrary, 
no  machine  in  existence  is  mechanically  simpler  than  the 
dynamo  or  motor.  The  only  wearing  parts  about  the  ma- 
chine, with  the  exception  of  the  commutator  and  brushes, 
which  are  specially  made  to  stand  almost  unlimited  wear 
without  interfering  with  the  action  of  the  machine,  are  the 
two  bearings.  In  this  respect,  therefore,  the  dynamo  or 
motor  is  as  simple  as  an  ordinary  grindstone,  and  infinitely 
simpler  than  a  steam  engine,  which  often  has  a  dozen  or 
more  oil  cups  and  several  dozen  wearing  parts.  Even  a 
sewing  machine  is  far  more  complicated  mechanically  than 
any  dynamo  or  motor.  In  fact,  it  would  be  useless  to 
attempt  to  give  a  method  for  detecting  and  curing  dynamo 
and  motor  troubles  if  it  were  not  for  the  fact  that  these 
machines  consist  of  very  few  parts,  which  makes  it  reason- 
ably possible  to  locate  the  trouble. 

The  rules  are  made,  as  far  as  possible,  self-explanatory, 
but  a  statement  of  the  general  plan  followed  and  its  most 
important  features  will  facilitate  the  understanding  and 
use  of  the  table. 

USE  OF  THE  TABLE  OF  TROUBLES. 

In  the  use  of  this  table  the  principal  object  should  al- 
ways be  to  clearly  separate  the  various  causes  and  effects 


of  Troubles  in  Dynamos  or  Motors.  3 

from  each  other.  A  careful  and  thorough  examination 
should  first  be  made,  and  as  far  as  possible  one  should  be 
perfectly  sure  of  the  facts,  rather  than  attempt  to  guess 
what  they  are  and  jump  at  conclusions.  Of  course  general 
precautions  and  preventive  measures  should  be  taken 
before  any  troubles  occur,  if  possible,  rather  than  wait  until 
a  difficulty  has  arisen.  For  example,  see  that  machine  is 
not  overloaded  or  running  at  too  high  voltage,  and  make 
sure  that  the  oil  cups  are  not  empty.  Neglect  and  care- 
lessness with  any  machine  are  usually  and  deservedly  fol- 
lowed by  accidents  of  some  sort. 

The  general  plan  of  the  table  is  to  divide  all  dynamo 
and  motor  troubles  which  are  liable  to  occur  into  eight  classes, 
the  headings  of  which  are  the  eight  most  important  and  obvi- 
ous bad  effects  produced  in  these  machines,  viz  : 

No.  1.  Sparking  at  Commutator. 
No.  2.  Heating  of  Armature. 
No.  3.  Heating  of  Field  Magnets. 
No.  d.  Heating  of  Bearings. 
No.  #.  Noise. 

No.  6.  Speed  too  high  or  low. 
No.  7.  Motor  stops  or  fails  to  start. 
No.  8.  Dynamo  fails  to  generate. 

Any  one  of  these  general  effects  is  \  ^ry  obvious,  even 
to  the  casual  observer,  and  still  more  so  to'  any  one  making 
a  careful  examination,  and  every  one  of  these  effects  is 
perfectly  distinguishable  from  any  of  the  others  without 
the  least  difficulty.  Hence,  this  classification  is  perfectly 
definite  and  makes  it  easy  to  tell,  almost  at  the  first  glance, 
under  which  one  of  these  heads  any  trouble  belongs,  thereby 
eliminating  about  seven-eighths  of  the  possible  cases.  The 
next  step  is  to  find  out  which  particular  one  of  the  six  or 
eight  cases  in  this  class  is  responsible  for  the  trouble.  This, 


4  Localization  and  Remedy 

of  course,  requires  more  careful  examination,  but,  never- 
theless, can  be  done  with  comparative  ease  in  most  cases. 
Of  course  one  cause  may  produce  two  effects,  and,  vice- 
versa,  one  effect  may  be  produced  by  two  causes  ;  but  the 
table  is  arranged  to  cover  this  fact  as  far  as  possible.  In 
a  very  complicated  or  difficult  case  it  is  well  to  read 
through  the  entire  table  and  note  what  causes  can  possibly 
apply,  and  they  will  generally  not  be  more  than  two  or 
three,  then  proceed  to  pick  out  the  particular  one  by  fol- 
lowing the  directions  which  show  how  each  case  may  be 
distinguished  from  any  other.  The  table  is  intended  for 
the  use  of  those  who  build,  test,  install,  own  or  operate 
electrical  machinery,  and  all  statements  apply  equally  well 
to  both  dynamos  and  motors,  unless  otherwise  specially 
noted. 


of  Troubles  in  Dynamos  or  Motors. 


CHAPTER  I. 
SPARKING   AT   COMMUTATOR. 

1.  Cause. — Armature  carrying  too  much  current,  due 
to  (a)  overload  (for  example,  too  many  lamps  fed  by 
dynamo,  or  too  much  mechanical  work  done  by  constant- 
potential  motor);  or  (b)  excessive  voltage  on  a  constant- 
potential  circuit  or  excessive  amperes  on  a  constant- current 
circuit.  In  the  case  of  a  motor  on  a  constant-potential  cir- 
cuit, any  friction,  such  as  armature  striking  pole-pieces  or 
shaft  not  turning  freely,  will,  of  course,  have  the  same  effect 
as  overload  in  producing  excessive  current.  The  armature 
of  a  motor  on  a  constant- current  circuit  does  not  tend  to 
heat  more  when  overloaded,  because  the  current  and  the 
heat  it  produces  in  the  armature  (ca  u)  are  constant.  In 
fact,  armature  can  be  stopped  with  full  current  without 
injury  except  loss  of  ventilation. 

Symptom* — Whole  armature  becomes  overheated  and 
belt  very  tight  on  tension  side  and  sometimes  squeaks,  due 
to  slipping  on  pulley.  Overload  due  to  friction  is  detected  by 
stopping  machine  and  then  turning  it  slowly  by  hand.  See 
Heating  of  Bearings  and  Noise,  No.  2. 

REMEDY. — (c)  Reduce  the  load;  (d)  decrease  the  size 
of  driving  pulley,  or  (e)  increase  the  size  of  driven  pulley; 
(f)  decrease  magnetic  strength  of  the  field  in  the  case  of  a 
dynamo  or  increase  it  in  the  case  of  a  motor.  If  excess  of 
current  cannot  satisfactorily  be  overcome  in  any  of  the 
above  ways  it  will  probably  be  necessary  to  change  the 
machine  or  its  winding.  Overload  due  to  friction  is  elimi- 
nated as  described  under  Heating  of  Bearings  and  Noise, 
No.  2. 


6  Localization  and  Remedy 

2*  Cause, — Brushes  not  set  at  the  neutral  point. 

Symptom. — Sparking  varied  by  shifting  the  brushes 
with  rocker-arm. 

REMEDY. — Carefully  shift  brushes  back  and  forth 
until  sparking  is  reduced  to  a  minimum.  This  may  be 
done  by  simply  moving  the  rocker-arm,  provided  the 
brushes  are  set  so  as  to  touch  diametrically  opposite  points 
on  the  commutator.  If  the  brushes  are  not  exactly  oppo- 
site they  should  be  made  so,  the  proper  points  of  contact 
being  determined  by  counting  the  commutator  bars  or 
measuring  with  a  piece  of  string  or  paper. 


B 


Fias.  1,  2  AND  3. — 1.  COMMUTATOR  IN  GOOD  CONDITION.    2.  COM- 
MUTATOR IN  BAD  CONDITION.    3.  HIGH  BAR  ON  COMMUTATOR. 

3.  Cause. —  Commutator  (a)  rough,  (fy  eccentric,  or  (c) 
has  one  or  more  "high  bars" projecting  beyond  the  others. 


or  (d)  one  or  more  flat  bars,  commonly  called 

any  one  of  which  causes  brush  to  vibrate  or  to  be  actually 

thrown  out  of  contact  with  commutator.    (Figs.  1,  2  and  3.) 

Symptom. — (e)  Note  whether  there  is  a  glaze  or 
polish  on  the  commutator,  which  shows  smooth  working; 
(/)  touch  revolving  commutator  with  tip  of  finger  and  the 
least  roughness  is  perceptible.  If  the  machine  runs  at  high 
voltage  (over  250)  the  commutator  should  be  touched  with 


of  Troubles  in  Dynamos  or  Motors.  7 

a  small  stick  or  quill  to  avoid  danger  of  shock.  In  the  case 
of  an  eccentric  commutator,  careful  examination  shows  a 
rise  and  fall  of  the  brush  when  commutator  turns  slowly. 

REMEDY. — Smooth  the  commutator  with  file  or  fine 
sandpaper  (in  latter  case  be  careful  to  remove  sand  and 
never  use  emery),  or  if  commutator  is  very  rough  or  eccen- 
tric, turn  it  off  with  a  fine  cut  in  a  lathe. 

In  order  to  have  the  commutator  wear  smooth  and  work 
well  it  is  desirable  to  have  the  armature  shaft  move  freely 
back  and  forth  about  one-sixteenth  or  an  eighth  of  an  inch 
in  the  bearings,  and  the  position  of  the  bearings,  pulley, 
collars  and  shoulders  on  the  shaft  and  of  the  machine  with 
respect  to  the  belt  should  be  such  as  to  cause  this  to  take 
place  of  itself.  (See  Heating  of  Bearings,  No.  6.) 


4.  Cause. — Brushes  make  poor  contact  with  commu- 
tator. 

Symptom. — Close  examination  shows  that  brushes 
touch  only  at  one  corner,  or  only  in  front  or  behind,  or 
there  is  dirt  on  surface  of  contact. 

REMEDY. — File,  bend,  adjust  or  clean  brushes  until 
they  rest  evenly  on  commutator  with  considerable  surface 
of  contact  and  with  sure  but  light  pressure. 


5.  Cause. — Short-circuited  coil  in  armature. 

Symptom,. — The  particular  commutator  bar  connected 
to  short-circuited  coil  is  burnt  by  the  spark  which  occurs 
when  brush  passes  over  it. 

The  short-circuited  coil  is  heated  much  more  than  the 
others,  and  is  very  apt  to  be  burnt  out  entirely;  therefore 
stop  machine  immediately.  If  necessary  to  run  machine 
to  locate  the  short  circuit,  one  or  two  minutes  is  long 
enough,  but  it  may  be  repeated  until  the  heat  of  the  short- 
circuited  coil  is  found  by  touching  the  armature  all  over. 


8  Localization  and  Remedy 

Considerable  power  is  required  to  run  armature  free.  An 
iron  screw-driver  or  other  tool  held  near  the  revolving 
armature  vibrates  perceptibly  as  short-circuited  coil 
passes.  Current  pulsates  and  torque  is  unequal  at  dif- 
ferent parts  of  a  revolution,  these  being  particularly 
noticeable  when  armature  turns  rather  slowly.  If  a  large 
portion  of  the  armature  is  short  circuited  the  heating  is 
distributed  and  harder  to  locate.  In  this  case  a  motor 
runs  very  slowly  with  very  little  power,  but  full  field  mag- 
netism. (For  dynamos,  see  Dynamo  Fails  to  Generate, 
No.  3.) 

REMEDY. — A  short  circuit  is  often  caused  by  a  piece 
of  solder  or  other  metal  getting  between  the  commutator 
bars  or  their  connections  with  the  armature,  and  some- 
times the  insulation  between  these  bars  is  bridged  over  by 
a  particle  of  metal.  In  any  such  case  the  trouble  is  easily 
found  and  corrected.  If,  however,  the  short  circuit  is  in 
the  coil  itself,  the  only  real  cure  is  to  rewind  the  coil. 

In  an  emergency  a  short-circuited  coil  may  be  tem- 
porarily cut  out  by  connecting  together  the  two  commu- 
tator bars  to  which  its  terminals  are  connected  or  the  two 
adjacent  coils,  as  described  in  the  Remedy  for  Sparking, 
No.  6.  But  be  sure  to  unwind  or  open  the  circuit  of  the 
short-circuited  coil,  as  otherwise  the  trouble  will 
continue.  

6.  Cause. — Broken  circuit  in  armature. 

Symptom. — Commutator  flashes  violently  while  run- 
ning and  commutator  bar  nearest  the  break  is  badly  cut 
and  burnt,  but  in  this  case  no  particular  armature  coil 
will  be  heated,  as  in  the  last  case  (No.  5),  and  the  flashing 
will  be  very  much  worse,  even  when  turning  slowly.  This 
trouble,  which  might  also  be  confounded  with  a  bad  case 
of  "high  bar"  or  eccentricity  in  commutator  (Sparking, 
No.  3),  is  distinguished  from  it  by  slowly  turning  the 
armature,  when  violent  flashing  will  continue  if  circuit  is 
broken,  but  not  with  eccentric  commutator  or  even  with 


of  Troubles  in  Dynamos  or  Motors.  9 

"  high  bar,"  unless  the  latter  is  very  bad,  in  which  case  it  is 
easily  felt  or  seen. 

REMEDY. — The  broken  circuit  is  usually  found 
where  armature  wires  connect  with  commutator,  and  not 
in  the  coil  itself,  and  the  break  may  be  repaired  or  the 
loose  wire  may  be  resoldered  or  screwed  back  in  place. 
If  the  broken  commutator  connection  cannot  be  fixed,  then 
connect  the  disconnected  bar  to  the  next  by  solder,  or 
"stagger"  the  brushes;  that  is,  put  one  a  little  forward 
and  the  other  back  so  as  to  bridge  over  the  break  (Fig.  4). 
If  the  break  is  in  the  coil  itself,  rewinding  is  generally  the 
only  cure.  But  this  may  be  remedied  temporarily  by  con- 
necting together  by  wire  or  solder  the  two  commutator  bars 


FIG.  4. — STAGGERED  BRUSHES. 

or  coil  terminals  between  which  the  break  exists.  It  is  only 
in  an  emergency  that  armature  coils  should  be  cut  out  or 
commutator  bars  connected  together,  or  other  makeshifts 
resorted  to,  but  it  sometimes  avoids  a  very  undesirable 
stoppage.  A  very  rough,  but  nevertheless  quick  and 
simple,  way  to  connect  two  commutator  bars  is  to  hammer 
or  otherwise  force  the  coppers  together  across  the  mica 
insulation  at  the  end  of  the  commutator.  This  can  be 
afterwards  easily  picked  out  and  smoothed  over.  In 
carrying  out  any  of  these  methods  care  should  be  taken 
not  to  short  circuit  an  armature  coil,  which  would  cause 
Sparking,  No.  5. 


10  Localization  and  Remedy 

7.  Cause. —  Weak  field  magnetism, 

Symptom* — Pole-pieces  not  strongly  magnetic  when 
tested  with  a  piece  of  iron.  Point  of  least  sparking  is 
shifted  considerably  from  normal  position,  due  to  relatively 
strong  distorting  effect  of  armature  magnetism.  Speed  of 
a  motor  is  usually  high  unless  magnetism  is  very  weak  or 
nil,  in  which  case  a  motor  may  run  slow,  stop,  or  even  run 
backwards.  A  dynamo  fails  to  generate  the  full  E.  M.  F. 
or  current.  The  particular  cause  of  trouble  may  be  found 
as  follows :  A  broken  circuit  in  the  field  is  found  by  purposely 
opening  the  field  circuit  at  some  point,  taking  care  to  first 
disconnect  armature  (by  putting  wood  under  the  brushes,  for 
example)  and  to  use  only  one  hand  to  avoid  shock,  and  if 
there  is  no  spark  there  must  be  a  broken  circuit  some- 
where. A  short  circuit  is  found  by  measuring  the  resist- 
ance roughly  to  see  if  it  is  very  much  less  than  it  should 
be,  and  usually  a  short  circuit  is  confined  to  one  magnet 
and  will  therefore  weaken  that  particular  one  most,  and  a 
piece  of  iron  held  half-way  between  the  pole-pieces  will  be 
attracted  to  one  more  than  the  other.  "Grounding"  is 
practically  identical  with  short  circuiting,  since  one  ground 
would  not  produce  this  effect  until  another  occurred,  and 
then  we  should  have  a  double  ground,  which  is  equivalent 
to  a  short  circuit. 

REMEDY. — A  broken  or  a  short. circuit  or  a  ground 
is  easily  repaired  if  it  is  external  or  accessible.  If  it  is 
internal  the  only  remedy  is  to  rewind  the  faulty  coil. 

(See  Speed  Too  High  or  Low  ;  Motor  Stops  or  Fails  to 
Start  5  Dynamos  Fail  to  Generate.) 


of  Troubles  in  Dynamos  or  Motors  11 


CHAPTER  II. 
HEATING  IN  DYNAMO  OR  MOTOR. 

GENERAL   INSTRUCTIONS. 

THE  degree  of  heat  that  is  injurious,  or  even  objection- 
able, in  any  part  of  a  dynamo  or  motor  is  fortunately  very 
easily  and  quite  definitely  determined  in  ordinary  practice. 
All  that  is  necessary  is  to  place  the  hand  on  the  various 
parts,  and  if  it  can  remain  without  discomfort  the  heat  is  en- 
tirely harmless.  But  if  the  heat  is  unbearable  for  more  than 
a  few  seconds,  the  safe  limit  of  temperature  has  been  passed, 
and  it  should  be  reduced  in  some  of  the  ways  that  are 
given  below.  If  the  heat  has  become  so  great  as  to  pro- 
duce an  odor  or  smoke,  the  safe  limit  has  been  far  exceeded, 
and  the  current  should  be  shut  off  and  the  machine  stopped 
immediately,  as  this  indicates  a  serious  trouble,  such  as  a 
short-circuited  coil  or  a  tight  bearing.  The  machine  should 
not  again  be  started  until  the  cause  of  the  trouble  has  been 
found  and  positively  overcome.  Of  course  neither  water  nor 
ice  should  ever  be  used  to  cool  electrical  machinery,  except 
possibly  the  bearings  in  large  machines,  where  it  can  be 
applied  to  the  bearings  as  a  cooler  without  danger  of  wet- 
ting the  other  parts. 

The  above  simple  method  will  answer  in  ordinary  cases, 
but,  of  course,  the  sensitiveness  of  the  hand  differs,  and  it 
makes  a  very  great  difference  in  the  feeling  whether  bare 
metal  or  cotton-covered  wire  is  touched.  The  back  of 
the  hand  is  more  sensitive  and  less  variable  than  the  palm 
for  this  test.  But  for  accurate  results,  a  thermometer 
should  be  applied  and  covered  with  waste  or  cloth  to  keep 
in  the  heat.  In  proper  working  the  temperature  of  no  parts 
of  the  machine  should  rise  more  than  40°  C.  or  72°  F. 


1&  Localization  and  Remedy 

above  the  temperature  of  the  surrounding  air.  If  the 
actual  temperature  of  the  machine  reaches  boiling  point, 
100°  C.  or  212°F.,  it  is  seriously  high. 

It  is  very  important  in  all  cases  of  heating  to  locate  cor- 
rectly the  source  of  heat  in  the  exact  part  in  which  it  is 
produced.  It  is  a  common  mistake  to  suppose  that  any 
part  of  a  machine  which  is  found  to  be  hot  is  the  seat  of  the 
trouble.  In  every  case  all  parts  of  the  machine  should  be 
felt  to  find  which  is  the  hottest,  since  heat  generated  in  one 
part  is  rapidly  diffused  throughout  the  entire  machine.  It 
is  generally  much  surer  and  easier  in  the  end  to  make  ob- 
servations for  heating  by  starting  with  the  whole  machine 
perfectly  cool,  which  is  done  by  letting  it  stand  for  one  or 
more  hours,  or  over  night,  before  making  the  examination. 
When  ready  to  try  it,  run  it  fast  for  three  to  five  minutes, 
then  stop  and  feel  all  parts  immediately.  The  heat  will 
then  be  found  in  the  right  place,  as  it  will  not  have  had  time 
to  diffuse  from  the  heated  to  the  cool  parts  of  the  machine. 
In  fact,  after  the  machine  has  run  some  time  any  heating 
effect  will  spread  until  all  parts  are  nearly  equal  in  tem- 
perature, and  it  will  then  be  almost  impossible  to  locate 
the  trouble 


6f  Troubles  in,  Dynamos  or  Motor*.  id 


CHAPTER  III. 
HEATING  OF  ARMATURE. 

1.  Cause.  —  Excessive    current     in     armature    coils. 
Symptom  and  Remedy  the  same  as  Sparking,  No.  1. 

2.  Cause.  —  /Short-circuited  armature  coils.    Symptom 
and  Remedy  the  same  as  Sparking,  No.  5. 

3.  Cause.  —  Moisture  in  armature  coils. 


.  —  Armature  requires  considerable  power 
to  run  free.  Armature  steams  when  hot,  or  feels  moist. 
This  is  really  a  special  case  of  No.  2,  as  moisture  has  the 
effect  of  short  circuiting  the  coils  through  the  insulation. 
Measure  insulation  of  armature. 

REMEDY.  —  Dry  the  armature  in  a  warm,  but  not  hot, 
place.  This  may  be  done  very  neatly  by  passing  a  current 
through  the  armature,  which  should  be  regulated  so  as  not 
to  exceed  the  usual  armature  current. 

4.  Cause.  —  Foucault  currents  in  armature  core. 

Symptom.—  Iron  of  armature  core  hotter  than  coils 
after  a  short  run,  and  considerable  power  required  to  run 
armature  when  field  is  magnetized  and  no  load  on  armature. 
This  may  be  distinguished  from  No.  2  by  absence  of  spark- 
ing and  absence  of  excessive  heat  in  a  particular  coil  or 
coils  after  a  short  run. 

REMEDY.  —  Armature  core  should  be  laminated  more 
perfectly,  which  is  a  matter  of  first  construction. 


14  Localization  and  Remedy 


CHAPTER  IV. 
HEATING   OF   FIELD  MAGNET. 

1.  Cause. — Excessive  current  infield  circuit. 
Symptom. — Field  coils  too  hot  to  keep  the  hand  on. 

REMEDY. — In  the  case  of  a  shunt-wound  machine 
decrease  the  voltage  at  terminals  of  field  coils,  or  increase 
the  resistance  in  field  circuit  by  winding  on  more  wire  or 
putting  resistance  in  series.  In  the  case  of  a  series- wound 
machine,  shunt  a  portion  of,  or  otherwise  decrease,  the  cur- 
rent passing  through  field,  or  take  a  layer  or  more  of  wire 
off  the  field  coils,  or  rewind  with  coarser  wire.  This 
trouble  might  be  due  to  a  short  circuit  in  field  coils  in  the 
case  of  a  shunt-wound  dynamo  or  motor,  and  would  be  in- 
dicated by  one  pole-piece  with  the  short-circuited  coil  being 
weaker  than  the  other;  one  of  the  coils  would  also  probably 
be  hotter  than  the  other;  but  this  can  only  be  remedied  by 
rewinding  short-circuited  coil.  Measure  resistance  of  field 
coils  to  see  if  they  are  nearly  equal.  If  the  difference  is 
considerable  (  i.  e.  more  than  5  or  10  percent.)  it  is  almost 
a  sure  sign  that  one  or  both  coils  are  short  circuited  or 
double-grounded. 

2.  Cause. — Foucault  currents  in  pole-pieces. 

Symptom. — Pole-pieces  hotter  than  coils  after  a 
short  run.  The  pole-pieces  being  bare  metal  and  coils 
being  covered,  when  making  comparison  it  is  of  course 
necessary  to  keep  hand  on  coils  some  time  before  full  effect 
is  reached,  and  even  then  it  is  reduced. 

REMEDY. — This  trouble  is  either  due  to  faulty  de- 
sign and  construction,  which  can  only  be  corrected  by  re- 


of  Troubles  in  Dynamos  or  Motors.  15 

building,  or  else  it  is  caused  by  fluctuations  in  the  current. 
The  latter  can  be  detected,  if  the  variations  are  not  too 
rapid,  by  putting  an  ammeter  in  circuit,  or  rapid  variations 
may  be  felt  by  holding  a  piece  of  iron  near  the  pole-pieces 
and  noting  whether  it  vibrates.  A  direct  current  does  not 
usually  vary  enough  to  cause  this  trouble,  but  in  the  case  of 
an  alternating  current  it  is  necessary  to  use  laminated  fields 
to  avoid  great  heating,  and  the  ordinary  arc  currents  fluc- 
tuate enough  to  cause  some  trouble  in  this  way. 


3.  Cause. — Moisture  in  field  coils. 

Symptom. — Field-circuit  tests  lower  in  resistance 
than  normal  in  that  type  of  machine,  and  in  the  case  of 
shunt-wound  machines  the  field  takes  more  than  the 
ordinary  current.  Field  coils  steam  when  hot,  or  feel  moist 
to  hand. 

REMEDY. — Dry  the  field  coils  in  a  warm  but  not  hot 
place.  This  may  be  done  simply  by  passing  a  current 
through  the  field  coils,  which  must  be  regulated  BO  as  not 
to  exceed  the  usual  field  current. 


16  LccaUzation  and  Remedy 


CHAPTER  V. 
HEATING  OF  BEARINGS. 

1.  Cause. — Lack  of  oil. 

Symptom. — Shaft  and  bearing  look  dry.  Shaft 
usually  turns  stiffly.  Oil  cup  or  reservoir  empty. 

REMEDY. — Supply  oil,  and  also  make  sure  that  oil 
passages  as  well  as  feeding  or  self-oiling  devices  work 
freely,  and  that  the  oil  cannot  leak  out.  This  last  fault 
sometimes  causes  oil  to  fail  sooner  than  attendant  expects. 

2.  Cause, —  Grit  or  other  foreign  matter  in  bearings. 

Symptom,. — Best  detected  by  removing  shaft  or 
bearing  and  examining  both.  Any  grit  can  of  course  easily 
be  felt,  and  will  also  scratch  the  shaft. 


Fia.  5.— SHAFT  ROUGH  OB  Cur. 

REMEDY. — Remove  shaft  or  bearing,  clean  both  very 
carefully  and  see  that  no  grit  can  get  in.  Place  machine  in 
dustless  place  or  box  it  in. 

3.  Cause. — Shaft  rough  or  cut.     (Fig.  5.) 

Symptom. — Shaft  will  show  grooves  or  roughness, 
and  will  probably  revolve  stiffly. 

REMEDY. — Turn  shaft  in  lathe  or  smoothe  with  fine 
file  and  see  that  bearing  is  smooth  and  fits  shaft. 


of  Troubles  in  Dynamos  or  Motors. 


17 


4.  Cause. — Shaft  and  bearing  Jit  too  tight. 
Symptom. — Shaft  hard  to  revolve  by  hand. 
REMEDY.— Turn  or  file  down  shaft  in  lathe,  or  scrape 

or  ream  out  bearings. 

5.  Cause. — Shaft  "sprung"  or  bent. 

Symptom. — Shaft  hard  to  revolve  and  usually  sticks 
much  more  in  one  part  of  revolution  than  in  another. 


FKJ.  6.— ARMATURE  WITH  GOOD  CLEARANCE  AT  C  C. 

REMEDY. — It  is  almost  impossible  to  straighten  a 
.bent  shaft.  It  might  be  bent  or  turned  true,  but  prob- 
ably a  new  shaft  will  be  necessary. 

6.  Cause. — Searings  out  of  line. 

Symptom. — Shaft  hard  to  revolve,  but  is  much 
relieved  by  loosening  screws  which  hold  bearings  in  place. 
Bearing  sometimes  moves  perceptibly  when  loosened,  even 
when  motor  is  not  running,  and  belt  is  off. 

REMEDY. — Loosen  bearings  by  partly  unscrewing 
bolts  or  screws  holding  them  in  place,  and  find  their  easy 


18 


Localization  and  Remedy 


and  true  position,  which  may  either  require  it  to  be  moved 
sideways  or  up  and  down  ;  then  file  the  screw-holes  of  the 
bearings  or  raise  or  lower  the  bearings,  as  may  be  neces- 
sary, to  make  them  occupy  right  position  when  screws  are 
tightened. 

7.  Cause.  —  Thrust  or  pressure  of  pulley,  collar  or 
shoulder  on  shaft  against  one  or  both  of  the  bearings. 
(Figs.  6  and  7.) 


.  —  Move  shaft,   while  revolving,  back  and 
forth  with  the  finger  or  a  stick  applied  to  the  end,  and  note 


FIG.  7. — &    IA.TURE  FORCED  AGAINST  BEARING. 


if  collar  or  shoulder  tends  to  be  pushed  or  drawn  against 
either  bearing.  A  dynamo  or  motor  shaft  should  always 
be  capable  of  moving  freely  back  and  forth  a  sixteenth  or 
eighth  of  an  inch  to  make  commutator  and  bearings  wear 
smooth  (See  Sparking,  No.  3).  If  this  does  not  occur  it 
should  be  relieved  in  one  of  the  following  ways: 

REMEDY. — Line  up  the  belt,  shift  collar  or  pulley, 
turn  off  shoulder  on   shaft   or  file  off  bearing  until  the 


of  Troubles  in  Dynamos  or  Motors.  19 

shoulder  does  not  touch  when  running  or  until  pressure  is 
relieved. 


8.  Cause. — Too  great  load  or  strain  on  the  belt. 

Symptom* — Great  tension  on  belt.  In  this  case 
pulley  bearing  will  probably  be  very  much  hotter  than  the 
other  and  also  worn  elliptical,  as  indicated  in  Fig.  8,  in 
which  case  the  shaft  may  be  shaken  in  the  bearing  in  the 
direction  of  the  belt  pull,  provided  the  machine  has  been 
running  long  enough  to  wear  the  bearings. 


Fia.  8.— BEARING  WORN  ELLIPTICAL. 

REMEDY. — Reduce  load  or  belt  tension,  or  use  larger 
pulleys  and  lighter  belt  or  even  gearii  <*  so  as  to  relieve 
side  strain  on  shaft. 


9.  Cause.  —  Armature  too  near  one  pole-piece,  produc- 
ing much  greater  magnetic  attraction  on  nearer  side. 


.  —  Examine  the  clearance  of  armature  and 
see  if  it  is  uniform  on  all  sides.  Charge  and  discharge  the 
field  magnet,  the  armature  being  disconnected  (by  putting 
paper  under  one  brush),  and  see  if  armature  seems  to  be 
drawn  to  one  side  and  turns  very  much  less  easily  when 
field  is  magnetized. 


20  Localization  and  Remedy 

REMEDY. — This  fault  is  due  to  an  inherent  defect  in 
the  original  construction,  which  is  difficult  to  correct,  but 
in  cases  of  necessity  the  armature  can  be  centered  exactly 
in  the  field  by  moving  the  bearings,  which  may  be  done  by 
carefully  filing  the  holes  through  which  the  screws  pass  that 
hold  the  bearings  in  place,  or  the  pole-piece  may  be  filed 
away  where  it  is  too  near  the  armature.  It  is  sometimes 
possible  to  spring  the  pole-piece  further  away  from  the 
armature,  but  it  is  difficult  and  dangerous  to  attempt. 


of  Troubles  in  Dynamos  or  Motors. 


CHAPTER  VI. 
NOISE. 

!•  Cause. —  Vibration  due  to  armature  or  pulley  being 
out  of  balance. 

Symptom. — Strong  vibration  felt  when  hand  is  placed 
on  machine  while  running.     Vibration  changes  greatly  if 


FIG.  9.— METHOD  OP  BALANCING  ARMATURE. 

speed  is  changed,  and  sometimes  almost  disappears  at  cer- 
tain speeds. 

REMEDY. — Armature  or  pulley  must  be  perfectly 
balanced  by  securely  attaching  lead  or  other  weight  on 
light  side,  which  can  be  found  by  trial.  The  easiest  method 
of  finding  in  which  direction  the  armature  is  out  of  balance 
is  to  take  it  out  and  rest  the  shaft  on  two  parallel  and 
horizontal  A-shaped  metallic  tracks  sufficiently  far  apart  to 
allow  armature  to  go  between  them  (Fig.  9).  If  the  armature 
is  then  slowly  rolled  back  and  forth,  the  heavy  side  will,  of 
course,  tend  to  turn  downward.  The  armature  and  pulley 
should  always  be  balanced  separately.  An  excess  of  weight 


on  one  side  of  pulley  and  an  equal  excess  of  weight  on  oppo- 
site side  of  armature  will  not  produce  a  balance  while  run- 
ning, though  it  may  appear  to  when  standing  still;  on  the 
contrary,  it  will  give  the  shaft  a  strong  tendency  to 
"wobble."  A  perfect  balance  is  only  obtained  when  the 
weights  are  directly  opposite,  i.  e.,  in  the  same  line  perpen- 
dicular to  the  shaft. 


2.  Cause. — Armature  strikes  pole-pieces. 

Symptom. — Easily  detected  by  placing  the  ear  near 
the  pole-pieces  or  by  examining  armature  to  see  if  its  sur- 
face is  abraided  at  any  point,  or  by  examining  each  part 
of  the  space  between  armature  and  field,  as  armature  is 
slowly  revolved,  to  see  if  at  any  point  it  touches  or  is  so 
close  as  to  be  likely  to  touch  when  the  machine  is  running. 
It  is  unwise  to  have  a  clearance  of  less  than  one-sixteenth 
inch  full.  Also  turn  armature  by  hand  when  no  current  is 
on  and  note  if  it  sticks  at  any  point. 

REMEDY. — Bind  down  any  wire  or  other  part  of 
armature  that  may  project  abnormally,  or  file  out  pole- 
pieces  where  armature  strikes. 


3.  Cause. — Shaft  collars  or  shoulders,  hub  or  edges  of 
pulley  or  belt  rattling  against  bearings. 

Symptom.  —  Noise  stops  when  shaft  or  pulley  is 
pushed  lengthwise  away  from  one  or  the  other  of  the 
bearings.  (See  Heating  of  the  Bearings,  No.  7.) 

REMEDY. — Shift  collar  or  pulley,  turn  off  shoulder  on 
shaft,  file  or  turn  off  the  bearing,  move  pulley  on  shaft  or 
straighten  belt  until  they  do  not  strike  and  noise  ceases. 


of  Troubles  in  Dynamos  or  Motors.  23 

4.  Cause. — Rattling  due  to  looseness  of  screws  or  other 
parts. 

Symptom. — Close  examination  of  the  bearings,  shaft, 
pulley,  screws,  nuts,  binding-posts,  &c.,  or  touching  the 
machine  while  running,  or  shaking  its  parts  while  standing 
still,  will  usually  show  the  particular  parts  which  are  loose. 

REMEDY. — Tighten  up  the  loose  parts,  and  be  careful 
to  keep  them  all  in  place  and  properly  set  up.  It  is  very 
easy  to  guard  against  the  occurrence  of  this  trouble, 
which  is  very  common,  by  simply  examining  the  various 
screws  and  other  parts  each  day  before  the  machine  is 
started. 


5.  Cause. — Singing  or  hissing  of  brushes  on  commu- 
tator^ usually  occasioned  by  rough  or  eccentric  commutator 
(see  Sparking  at  Commutator,  No.  3),  or  by  tips  of  brushes 
not  being  smooth,  or  the  layers  of  a  copper  brush  not  being 
held  together  and  in  place;  with  carbon  brushes,  hissing 
will  be  caused  by  the  use  of  carbon  which  is  gritty  or  too 
hard.  Vertical  carbon  brushes  or  inclined  brushes  running 
backward  are  apt  to  squeak  or  sing. 

Symptom. — Sound  of  high  pitch  and  easily  located 
by  putting  the  ear  near  the  commutator  while  it  is  running, 
and  by  lifting  off  the  brushes  one  at  a  time. 

REMEDY. — Apply  a  very  little  oil  to  the  commutator 
with  the  finger  or  a  rag.  Adjust  brushes  or  smooth  com- 
mutator by  turning,  filing  or  fine  sandpaper,  being 
careful  to  clean  thoroughly  afterwards.  Carbon  brushes 
are  apt  to  squeak  in  starting  up  or  at  slow  speed.  This 
decreases  at  full  speed,  and  can  usually  be  reduced  by 
moistening  carbon  brush  with  oil,  care  being  taken  not 
to  have  any  drops  or  excess  of  oil.  Shortening  or  length- 
ening the  brushes  sometimes  stops  the  noise. 


24  Localization  and  Remedy 

6.  Cause. — Flapping  or  pounding  of  belt  joint  or 
lacing  against  pulley.  (Fig.  10.) 

Symptom. — Sound  repeated  once  for  each  complete 
revolution  of  the  belt,  which  is  much  less  frequent  than  any 
other  dynamo  or  motor  sound,  and  can  be  seen  or  easily 
counted. 

REMEDY. — Endless  belt  or  smoother  joint  in  belt. 
A  perfect  joint  and  a  straight,  smooth  belt  are  always  very 
desirable  for  dynamos  and  motors. 


7.  Cause. — Slipping  of  belt  on  pulley  due  to  overload. 
Symptom* — Intermittent  squeaking  noise. 


FIG.  10.— BAD  JOINTS  IN  BELT. 

REMEDY.— Tighten  the  belt,  or  reduce  the  load.  A 
wider  belt  may  be  required. 

8.  Cause. — Humming  of  armature  oore  teeth  (if  any) 
as  they  pass  pole-pieces. 

Symptom. — Pure  humming  sound  less  metallic  than 
No.  5. 

REMEDY. — Slope  ends  of  pole-pieces  so  that  arma- 
ture tooth  does  not  pass  edge  of  pole-piece  all  at  once. 
Decrease  the  magnetization  of  the  fields.  Increase  the 
cross-section  or  magnetic  capacity  of  the  teeth,  or  reduce 
that  of  the  body  of  the  armature,  which  is  a  matter  of 
first  construction. 


of  Troubles  in  Dynamos  or  Motors.  25 


CHAPTER  VII. 
SPEED  TOO  HIGH  OR  LOW. 

This  kind  of  trouble  in  either  dynamo  or  motor  is  a  seri- 
ous matter,  and  it  is  always  desirable,  and  generally  im- 
perative, to  shut  off  the  current  immediately  and  make  a 
careful  investigation  of  the  trouble. 

1.  Cause.  —  Overload,    (See  Sparking,  No.  1.) 


.  —  Armature  runs  more  slowly  than  usual, 
Bad  sparking  at  commutator.  Ammeter  indicates  excessive 
current.  Armature  and  bearings  heat.  Belt  very  tight  on 
tension  side. 

REMEDY.  —  Reduce  the  load  on  machine  by  taking  off 
lamps  in  the  case  of  a  dynamo,  or  mechanical  work  in  the 
case  of  a  motor  ;  decrease  the  diameter  of  driving  pulley 
or  increase  the  diameter  of  driven  pulley. 

£•  Cause.  —  Short  circuit  in  armature. 

Symptom  and  remedy  the  same  as  Heating  of  Armature, 

No.  2. 

3.  Cause.^-  Armature  runs  slowly  because  it  strikes 
pole-pieces.  Symptom  and  Remedy  the  same  as  Noise,  No.  2. 

4.  Cause.  —  Armature  runs  slowly  because  its  shaft 
does  not  revolve  freely  in  the  bearings. 

Symptom.  —  Armature  turns  hard  by  hand  ;  bearings 
and  shaft  heat  when  running. 


26  Localization  and  Remedy 

REMEDY. — Oil  the  bearings;  clean  and  smooth,  if 
necessary,  the  shaft  and  bearings;  line  up  the  bearings. 
See  Heating  of  Bearings,  all  cases. 


5.  Cause, — Field  magnetism  weak. 

This  has  the  effect  of  making  a  motor  run  too  fast  or 
too  slow,  or  in  some  cases  even  run  backwards,  but  makes 
a  dynamo  fail  to  "build  up"  or  excite  its  field  and  give 
the  proper  voltage. 

Symptom  and  Remedy  the  same  as  Sparking,  No.  7. 
(See  the  following  class  ;  also,  Dynamo  Fails  to  Generate.) 


of  Troubles  in  Dynamos  or  Motors.  27 


CHAPTER  VIII. 
MOTOR  STOPS  OR  FAILS  TO  START. 

This  trouble  is,  of  course,  an  extreme  case  of  the  previ- 
ous class  (Speed  too  High  or  Low),  but  it  is  made  a 
separate  class  because  it  is  so  perfectly  definite  and  re- 
quires somewhat  different  treatment.  This  heading  does 
not,  of  course,  apply  to  dynamos,  since  they  are  usually 
driven  positively  by  an  engine  and  do  not,  like  a  motor, 
depend  on  their  own  operation  for  their  motion. 

1.  Cause. —  Great  Overload.  (See  Sparking,  No.  1.) 
A  slight  overload  causes  motor  to  run  slowly,  but  an  ex- 
treme overload  will,  of  course,  stop  it  entirely  or  "  stall "  it. 

Symptom* — On  a  constant-current  circuit  no  harm 
results,  and  motor  starts  properly  when  load  is  reduced  or 
taken  off. 

On  a  constant-potential  circuit  the  current  is  very  ex- 
cessive, and  safety  fuse  melts,  or,  in  the  absence  or  failure 
of  the  latter  to  act,  armature  would  be  burnt  out. 

REMEDY. — Turn  off  switch  instantly,  reduce  or  take 
off  the  load,  replace  the  fuse  or  cut-out  if  necessary,  and 
turn  on  current  again,  just  long  enough  to  see  if  trouble 
still  exists. 


2.  Cause. —  Very  excessive  friction  due  to  shaft,  bear- 
ings or  other  parts  being  jammed,  or  armature  touching 
pole-pieces. 

Symptom. — Similar  to  previous  case,  but  is  distin- 
guished from  it  by  the  fact  that  armature  is  hard  to  turn 


28  Localization  and  Remedy 

by  hand,  even  when  load  is  taken  off.  Examination  shows 
that  shaft  is  too  large,  bent  or  rough,  or  bearing  too  tight, 
armature  touches  pole-pieces  or  other  impediment  to  free 
rotation.  (See  Heating  of  Bearings  and  Noise.) 

REMEDY. — Turn  current  off  instantly,  ascertain  and 
remove  cause  of  friction,  turn  on  current  again  just  long 
enough  to  see  if  trouble  still  exists. 


3,  Cause.  —  Circuit  open  due  to  (a)  safety  fuse 
melted,  (b)  wire  in  motor  broken  or  slipped  out  of  connec- 
tions, (c)  brushes  not  in  contact  with  commutator,  (d) 
switch  open,  (e)  circuit  supplying  motor  open,  (/)  failure 
at  generating  station. 


*  —  Distinguished  from  Nos.  1  and  2  by  the 
fact  that  if  load  is  taken  off  motor  still  refuses  to  start, 
and  yet  armature  turns  freely  by  hand. 

On  a  constant  current-circuit  the  switch  arcs  badly  when 
turned  on  if  motor  circuit  is  open;  but  there  is  no  current, 
motion  or  other  effect  in  motor.  On  a  constant-potential 
circuit,  field  circuit  alone  of  a  shunt  motor  may  be  open,  in 
which  case  pole-pieces  are  not  strongly  magnetic  when  tested 
with  a  piece  of  iron  ;  if  armature  circuit  is  at  fault  there 
is  no  spark  when  brushes  are  lifted,  and  if  both  are  with- 
out current  there  is  no  spark  when  switch  is  opened. 

REMEDY.  —  Turn  current  off  instantly.  Examine 
safety  fuse,  wires,  brushes,  switch  and  circuit  generally  for 
break  or  fault.  If  none  can  be  found  turn  on  switch  again 
for  a  moment,  as  the  trouble  may  have  been  due  to  a 
temporary  stoppage  of  the  current  at  the  station  or  on  the 
line.  If  motor  still  seems  dead,  test  separately  armature, 
field  coils  and  other  parts  of  circuit  for  continuity  with 
a  magneto  or  cell  of  battery  and  electric  bell.  (See  In- 
structions for  Testing.) 


of  Troubles  in  Dynamos  or  Motors.  29 

4.  Cause.  —  Wrong  connection,  or  complete  short  cir- 
cuit of  field,  armature  or  switch. 


.  —  Distinguished  from  Nos  1  and  2  in  the 
same  way  as  No.  3,  and  differs  from  No.  3  in  the  evidence 
of  strong  current  in  motor. 

On  a  constant-potential  circuit,  if  current  is  very  great, 
it  indicates  a  short  circuit.  If  the  field  is  at  fault  it  will 
not  be  strongly  magnetic. 

The  possible  complications  of  wrong  connections  are  so 
great  that  no  exact  rules  can  be  given.  Carefully  examine  and 
make  sure  of  the  correctness  of  all  connections  (see  Dia- 
grams of  Connections).  This  trouble  is  usually  inexcus- 
able, since  only  a  competent  person  should  ever  set  up  or 
change  the  connections  of  a  motor. 


30  Localization  and  Remedy 


CHAPTER  IX. 
DYNAMO  FAILS  TO  GENERATE. 

This  class  of  troubles  is,  of  course,  confined  to  dynamos 
and  corresponds  somewhat  to  the  previous  class  for  motors. 
This  trouble  is  almost  always  caused  by  the  inability  of 
the  machine  to  sufficiently  "  excite"  or  "build  up  "its 
own  field  magnetism.  The  proper  starting  of  a  dynamo 
requires  a  certain  amount  of  residual  magnetism,  which 
must  be  increased  to  full  strength  by  the  current  generated 
in  the  machine  itself. 


1.  Cause. — Reversed  residual  magnetism,  due  to  («) 
reversed  current  through  field  coils,  (b)  reversed  connec- 
tions, (c)  earth's  magnetism,  (d)  proximity  of  another 
dynamo,  (e)  brushes  not  in  the  right  position. 

Symptom. — Little  or  no  magnetic  attraction  when 
pole-pieces  are  tested  with  piece  of  iron. 

Magnetism  weaker  when  machine  is  running  and  field 
circuit  closed  than  when  machine  is  stopped  or  field  open, 
because  current  generated  tends  to  build  down,  as  it  were, 
or  neutralize  the  magnetism. 

REMEDY. — Send  a  magnetizing  current  from  another 
machine  or  battery  through  field  coils,  then  start  and  try 
machine ;  if  this  fails,  apply  the  current  in  the  opposite 
direction  and  try  machine  again. 

Reverse  field  and  armature  with  respect  to  each  other, 
i.  e.y  reverse  connections  of  either  one  or  shift  brushes. 


of  Troubles  in  Dynamos  or  Motors,  31 

2.  Cause. — Too  weak  residual  magnetism.  Symp- 
toms and  remedies  of  this  trouble  are  substantially  the 
same  as  in  the  previous  case,  but  the  attraction  for  a  piece 
of  iron  is  even  weaker — in  fact,  practically  nothing — 
when  the  machine  is  not  running. 


3.  Cause. — Short  circuit  in  the  machine  or  external 
circuit. 

This  applies  to  a  shunt-wound  machine,  and  has  the  effect 
of  preventing  the  voltage  and  the  field  magnetism  from 
building  up. 

Symptom* — Magnetism  weak,  but  still  quite  per- 
ceptible. 

REMEDY. — If  short  circuit  is  in  the  external  circuit, 
the  opening  of  the  latter  will  allow  the  dynamo  to  build  up 
and  generate  full  voltage.  If  the  short  circuit  is  within 
the  machine,  it  should  be  found  by  careful  inspection  or 
testing.  In  either  of  these  cases  do  not  connect  the  ex- 
ternal circuit  till  short  circuit  is  found  and  corrected. 

A  slight  short  circuit,  such  as  that  caused  by  a  defective 
lamp  socket  or  copper  dust  on  the  commutator,  may  pre- 
vent magnetism  from  building  up. 

(See  Sparking,  Nos.  5  and  7.) 


4.  Cause.— Field  coils  opposed  to  each  other. 

Symptom. — If  pole-pieces  are  approached  with  a  com- 
pass or  other  freely  suspended  magnet,  they  both  attract 
the  same  end  of  the  magnet,  showing  them  both  to  be  of 
the  same,  instead  of  opposite,  polarity. 

For  similar  reasons  the  pole-pieces  are  quite  strongly 
magnetic  when  tested  separately  with  a  piece  of  iron,  but 
show  less  attraction  when  the  same  piece  of  iron  is  applied 


32      Localization  and  Remedy  of  Troubles  in  Dynamos  or  Motors. 

to  both  pole-pieces  at  once,  whereas  the  attraction  should 
be  much  stronger.  In  multipolar  machines  these  tests 
should  be  applied  to  consecutive  pole-pieces. 

REMEDY.  —  Reverse  the  connections  of  one  of  the 
coils,  so  that  the  polarity  of  the  pole-pieces  is  opposite 
and  not  the  same. 

5.  Cause.  —  Open  circuit. 

(a)  Broken  wire  or  faulty  connection  in  machine,  (#) 
brushes  not  in  contact  with  commutator,  (c)  safety  fuse 
melted  or  absent,  (d)  switch  open,  (e)  external  circuit 
open. 


.  —  If  the  trouble  is  merely  due  to  the  switch 
or  external  circuit  being  open,  the  magnetism  will  be  at 
full  strength,  and  the  machine  itself  may  be  working  per- 
fectly,  but  if  the  trouble  is  in  the  machine,  the  field  mag- 
netism will  probably  be  very  weak. 

REMEDY.  —  Make  very  careful  examination  for  open- 
ing in  circuit  ;  if  not  found,  test  separately  the  field  coils, 
armature,  etc.,  for  continuity  with  magneto  or  cell  of  bat- 
tery and  electric  bell.  (See  Instructions  for  Testing.  ) 


CONCLUSION. 


It  is  obviously  difficult,  if  not  impossible,  in  the  treat- 
ment of  dynamo  and  motor  troubles  to  give  complete  di- 
rections for  locating  or  identifying  all  the  various  troubles  ; 
but  in  most  of  the  cases  this  will  be  found  possible  ;  and 
moreover,  it  is  a  fact  that  a  mere  list  of  these  troubles, 
particularly  if  it  is  systematically  arranged,  is  of  the 
greatest  help  in  overcoming  these  difficulties.  It  is  in  the 
promptness  and  intelligence  which  such  troubles  are 
dealt  with  that  the  ability  or  inability  of  a  man  is  most 
clearly  shown. 


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NIPIIEF,,  Prof.  F.  E.  Theory  of  Magnetic  Measure- 
ments. With  an  appendix  on  the  Method  of  Least  Squares. 
12mo,  cloth 1  00 

NO  AD,  H.  M.  The  Student's  Text-Book  of  Electricity.  A 
new  edition,  carefully  revised  by  W.  H.  Preece.  8vo, 
cloth,  illustrated 4  00 

POPE,  F.  S.  The  Modern  Practice  of  the  Electric  Tele- 
graph. New  edition,  entirely  rewritten,  1891.  8vo,  cloth.  1  50 

PLANTE,  G ASTON.  The  Storage  of  Electrical  Energy, 
and  Researches  in  the  Effects  Created  by  Currents  Combin- 
ing Quantity  with  High  Tension.  With  89  illustrations. 
Translated  from  the  French  by  Paul  B.  Elwell.  8vo, 
cloth 4  00 

SALOMONS,  SIR  DAVID.  Electric  Light  Installa- 
tions and  the  Management  of  Accumulators.  A  Practical 
Hand-book.  Sixth  edition,  revised  and  enlarged.  With 
99  illustrations.  348  pages,  12mo,  cloth 2  00 

SCHELLEN,  Dr.  H.  Magneto-Electric  and  Dynamo-Elec- 
tric Machines:  Their  Construction  and  Practical  Applica- 
tion to  Electric  Lighting  and  the  Transmission  of  Power. 
Translated  from  the  third  German  edition,  with  large  addi- 
tions and  notes  relating  to  American  Machines,  by  N.  S. 
Keith.  Vol.  I.,  with  353  illustrations.  8vo,  cloth 5  00 

THOMPSON,  SILVAN  US  P.  Dynamo-Electric 
Machinery.  A  Series  of  Lectures,  with  an  introduction 
by  Frank  L.  Pope.  16mo.  Numerous  illustrations,  boards. 
(Van  Nostrand's  Science  Series,  No.  66.). 50 

Recent  Progress  in  Dynamo-Electric  Machines:  being  a 

Supplement    to    Dynamo-Electric     Machinery.      16mo. 
(Van  Nostrand's  Science  Series,  No.  66.) .- . . .        50 

WA  TT,  A.  Electro  Deposition:  A  Practical  Treatise  on  the 
Electrolysis  of  Gold,  Silver,  Copper,  Nickel  and  other 
Metals  and  Alloys.  12mo,  cloth,  illustrated 3  50 

—  Electro-Metallurgy  Practically  Treated.  New  and  en- 
larged edition.  12mo,  cloth 1  00 

WA  LKER,  FREDERICK.  Practical  Dynamo  Build- 
ing for  Amateurs.  18mo,  boards 50 


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